What would you think of your mother in law wanted to invite 3 friends to your wedding, you’ve not met before

I'd say the choice is for her husband to be to make. If they're splitting the guest list allowance between families and he's willing to forgo having three of his own friends there to allow his mother to have her three friends there then that's fine. However if he's not OK with it then he needs to tell his mum no.

She should allow her MIL to have friends if she is contributing enough to cover their meals, especially if she is single. These women will have loved her husband to be growing up. I hope I’m invited to my best friends sons weddings even if I haven’t had a chance to meet the bride beforehand

I wish it had been three, I was handed a list of 50 people by my MIL and when some couldn’t come she wanted to give us more names to replace those who couldn’t come. Thankfully my FIL stepped in and told her to cop herself on. We paid for the entire days ourselves. The majority of them I had never met and my DH hadn’t seem some of them in years. One of the couples actually asked my DH and DBIL which one of them was the groom 🙄 While I wish I had put my foot down more on the day I didn’t really care and they kept my MIL entertained and out of my hair.

She should have hosted her own reception or celebration for you

I think this was mean of them

It was very traditional for parents to invite their friends to a wedding, especially in the days when they paid for it. It’s much less so now when generally the bride and groom
pay.

If they're the MIL's best friends, I'd say there's every chance they know one half of the couple pretty well.

Mine was told to uninvite them by now DH!
They also did not contribute a bean to our wedding either.

For the day they had to be people we both knew or at least had met.

For the evening it was more flexible, my mum invited some friends. It upset some relatives of my dad’s not invited to the day, but if we hadn’t seen each other in 10 years for them to have even met my partner then make it make sense?! Also my dad contributed about £200 to the day so he didn’t really have a say. If he had paid for half of the day, then I would have let him have more of a choice.

100%

Contributing financially does change things in my view. Very ungrateful to not even give you a plus one?! @MummyOre

Even if she didn't contribute a penny I think it was mean to have the mum/MIL attend alone.

She did. I let her. She paid. I wasn't introduced to them at the wedding and I still have never spoken to them 20 years later. It was a waste of her money but we weren't tight on space so she could do whatever she liked if she covered the cost.

Sometimes I don't know how people function. So much anxiety but they want a wedding and reception and can't handle three humans who are MILs friends.

My horrible MIL insisted on 2 of her stupid friends coming on condition of the donation she made towards the wedding. I am now nc with her, she's horrible, and I can't even remember her friends names, and never saw them again after the wedding. They took 2 of the 46 spaces we had, I am still pissed off about it tbh, and wish I'd told her to go fuck herself.

If there isn’t an issue with numbers then can’t see the problem esp as mil have contributed towards weeding

I had a ‘rule’ that I didn’t want anyone at my wedding I’ve never met - but that just meant we made an effort to meet the plus ones etc and more distant relatives before the wedding.

Would she consider that as a compromise??

Nope.

Is this in addition to the numbers you have already? Most people give their parents a number of guests, usually around ten, and say if they want any more, they need to pay. You say MIL-does that mean your husband's dad isn't around? In that case, I'd want to make sure she had as many people to support her as reasonable (obviously FIL might be there and you're just meaning these are her friends not his).
If you've already given her a lot of guests, all the numbers and everything is arranged, and she's suddenly dropped these 3, it's reasonable to ask her to pay for them, or not change things if already arranged.
If you've not let her invite anyone, that seems mean, unless there's a good reason like your husband to be warns they're trouble. You surely want her to enjoy the day as much as possible-she raised the man you're marrying.

‘Most people give their parents a number of guests, usually around ten, and say if they want any more, they need to pay’

I think this is an unusual way to go about things, frankly. Rarely this clear cut I would have thought.

If this is a traditional wedding and your father is paying, then your father decides who is invited.

Quote from the OP: Her dh to be slightly knows them but not much

When I got married mil invited her two closest friends and their husbands but I’d met them several times and one was dhs god mother. My mum invited her best friend who I’d known my entire life.

Agree completely. I (quietly) despair of the growing attitude that it's only the B & G who matter...

No reason why anyone would know their MIL’s friends. If she has a certain quota of invitations, she may as well ask who she likes.

They have a massive formal sit down wedding. Both have very large families and big groups of friends.

They didn't even invite all their aunts/uncles/cousins so were hardly going to invite my friends!