I always read threads like this as I'm still working on being the perfect widow and it will be 4 years in January.
It does seem that the widow pass expires at around the 6 month mark. And that one's actual loss is secondary to other people's expectations.
The expectation that you must remember you are not the only one grieving The expectation that you must be accommodating to everyone else's grief - if people want to talk about it, cry, or impose themselves on you, you suck it up because it's not all about you. If people want to pretend it hasn't happened and tell you to "dial it down" as one former friend did when I mentioned it was the first anniversary of my DPs collapse that lead to his death three weeks later, one must comply.
People just don't know what to do with you. They think they should do "something" and they make kind offers and include you, which you feel obliged to accept because you "know" life goes on, and even though it's like being outside a window in the cold watching a big happy party, Dickensian style, you try to join in. Then when you're nursing your drink in the corner because awkward conversations have happened, because you've been introduced to a new person, and can't really talk about much other than your current circumstances because that's how you get to know people, and they've awkwardly backed away for less intense interactions, even if you've tried dark and stoic humour, you notice a huddle of worried friends figuring out the next move. If you're on your thirsty or fourth drink, and perhaps a bit visibly wobbly, there's usually the offer of a lift home as someone's happens to be leaving and miraculously going your way. Or a taxi will be generously ordered.
So you tick "Merry Widow" off the list as not a good fit. Miss Haversham is a better look for a while, but this tends to prompt "intervention".
On the practical side, some people will help, say with moving house, or losing your business, and a sub section of those will never let you forget their willing sacrifices.
Occasionally you wonder if it would have been easier and preferable for all concerned if you'd just hopped into the grave at the funeral and had done with it.
It's also a bit like being pregnant. Everyone has an opinion, a story, advice, and gets weirdly invested if you try to just do your own thing, because they think that you've completely lost all shred of your own ability to make decisions, have your own opinions etc. Yes, grief impacts those things, but it's part of the processing and figuring out this unwanted new life that you're supposed to joyously embrace despite the fact that your heart is broken.
And so if anyone reads this far - some will get it, and know what I'm trying to convey. Some will eye roll (I predict a "melodrama", a "hyperbole" and several versions of self-centred) and suggest counselling (since I've lost my Dad, my MIL and an Uncle since April, don't worry I'm on it).
But for the OP - give MIL a break. How you handle this now will inform how your relationship with her, and family dynamics will evolve. Perhaps she is aware of your egg shell feelings. Do you know how stressful it is when people tip toe around as if you're an unexploded bomb? It's incredibly painful when grieving to realise you're a "problem" to people you love, because of something you can do very little about.
She may mask, she may go through the motions, she may project her sadness or grief onto you. And she may, like many widows find herself largely alone, hypervigilant about offending people, or thinking "fuck it".
If you want a good relationship with her moving forward tread carefully, and bear in mind this affects your DH too.