How can I be more forgiving with MIL

Your MIL is reaping what she sowed. You don't need to welcome her with open arms, she isn't the prodigal son.

It's a completely understandable, human response.

This. I came to write about my experience with abusive in laws who turned nice when they became frail and ill.

If they'd been kind and accepting instead, I'd have done anything for them. Now MIL has died & FIL is frail and just been admitted to age care. I won't even bother to see him unless unavoidable for DC sake. He's so nice to me now, but it's purely vulnerability talking. I wo8help. DH has to wear that as he knows he didn't stop them earlier on. I cannot forgive.

I agree with the poster above that you sound very kind and thoughtful.
There is a big difference between 'mistakes' wrt family members caused by genuine misunderstandings or miscommunication and being deliberately nasty, undermining and deliberately playing her children off against each other. That is manipulative and emotionally abusive.
From what you have said here, she is just an unpleasant person so your gut reactions to her are only natural. The fact that she is elderly and now widowed does not mean that she is suddenly a completely different character. Her circumstances have changed so she is changing her behaviour to try to take advantage of the new ones. Your DH is entitled to forgive and forget, she is his mum after all, but he should try to understand your feelings and not dictate how you should respond or behave. That is wrong of him.
If you had said that she apologised to you for her previous behaviour many years ago, given you some kind of explanation and been a loving and kind MIL for years, I am certain that you would have been able to move on. It is far harder to do so when the situation has never been discussed and no apology has been given.

I really like this framing. You're doing forgiveness even if you're not feeling it yet.

Yes, my MIL was entirely like this. Was foul to me and other females in the family who she thought she could dominate.
But as time passed ( decades) I discovered more and more how this was caused by severe MH issues.
Although she was in a very fortunate position outwardly, her inner self was in a terrible place. This inner self was making itself heard when she was cruel to other women.
Eventually she suffered a complete breakdown, which I wouldn’t wish on anyone.

Your motives are good. You sound kind and thoughtful. Your mil is lucky you’re even giving this some thought. You also know there are reasons why she’s doing this and not because she’s realised the error of her ways and suddenly likes you.
When there’s an issue like this, there needs to be an acknowledgment and repair work before you can easily move on and change. Would it help to have a conversation with your mil about it?

I find this quote helpful.
Forgive others, not because they deserve forgiveness but because you deserve peace.
Letting it go is an act of self care, holding on to the insult is only damaging yourself.

Same - I think if they are a nice/interested GP you can get over a lot of things.
The rude comments to me were then directed at DC. I took a massive step back, hardly saw her, which mean DC never saw her. Not that she cared.

I am in a similar situation with my mil who now is in her late 80s .
She was never a pleasant women , and has always been very self centred .
Even when her own children were still quite young , it was her she expected all the attention to ( told by someone close to the family )

She never wants to know what is going on in people's lives , never cares about what's going on in the wider world , no interest in issues etc .

Now she is older she is more needy , and it's difficult to want to help or even show any empathy towards her .

I do , but not for her . I tell myself I am helping the rest of the family , taking the burden off for them , not her .
Perhaps you can change your mindset by thinking that as well ?

Oh this entirely! I have found I just can’t get past it when someone treats me badly when I’ve been at my most vulnerable. I have experience of this too. The person was in a ‘better’ more comfortable position than me in every way, but chose that time to shit on me from a height. Hard to get past. I know I wouldn’t have done that to them - I’m kind to vulnerable people, but some take that opportunity to push someone down further. You rightly feel sorry for your 20 year old self, and because you’re a decent person, now the tables are turned you feel unable to dish out the same treatment to her.

That is so not true.
I have come to believe a geat deal of unpleasantness is down to MH troubles. That's definitely been the case in my family.
As the older generation goes into a different life stage, the MH problems brcome much less, can't explain why, but they do.
They basically get nicer because the thing that was driving them nuts, whether it's biological or environmental , goes away/lessens.
I do believe this.

completely off-topic sorry but @MegMortimer great username!

I don’t understand the forgiveness thing… You understand her, you tolerate her (or give the impression that you do). What has she done to create an environment where forgiveness is possible?

This visceral feeling of discomfort and anger is probably just years of conditioning, resulting from her behaviour. I guess it is like tensing up before being punched; you're expecting a verbal punch whenever you see her. If her behaviour has changed, it will perhaps take some time for you to really comprehend on a sub conscious level that you are not in for a kicking anymore.

Why do you have to try harder ?
Your marriage and responsibilities are towards her son and your children not her.
Be civil and polite but nothing more ,she should have though about that years ago, i bet your husband doesn't expect anything else from you after experiencing her awful behaviour.

It is a completely seperate issue if MIL is looking for care than forgiving past actions. You can actually decline any role a person tries to get you to take on anytime it doesn’t matter if the relationship is good, bad or indifferent.

Was she nice to her GC? If so I would go from there. Also go down the line of supporting DH.

Mine was not nice to DC and that is where the red line was crossed.

I say this because it is highly suspicious that your MIL has suddenly undergone a personality transplant. She has realised that she may well need help in the future and you're the most obvious candidate. But as others have said, it may help to reframe your feelings towards her as pity.

@MegMortimerWhy? I didn’t take on that role. Having a better relationship doesn’t mean you end up as a carer.

I predict a health crisis with your MIL within the next couple of years, which will necessitate your taking on the role of carer, OP.

I doubt very much she and your father in law ever meant anything in the way you took it. They wouldn't have understood a lot of what you did anyway.

It was a long time ago and you say she has been different since widowed. That struck a chord with me because my mother was different, far better, later on in life and became more insightful.

However, it's a good idea to forgive, no point in hanging on to past hurts which I doubt were deliberate; she was probably more tactless than spiteful.

Let bygones by bygones and move on.

My MIL threw her son out of the house when she knew he was dating a white single mother. I let it go, 15yrs after we split I still keep in touch. Her way of life / community / religion is a lot different to mine and I like to think I taught her to not judge a book by its cover

I agree with this.

IMO, why hold onto negative feelings and judgements? You wanted her to be nice and she wasn't. Well, now she is being nice. Just learn to take pleasure in that.
I am talking from experience btw. I had the same treatment, though my MIL died a few years ago.
Just look on the bright side. If you find yourself cringing inside, take a few deep breaths and think of something pleasant. It's not that hard, honestly.