Big argument with daughter.

She's obviously struggling ,she's NOT you and how she copes or not will be different from how you coped.She needs someone to rant at that wont take offence or judge and she thinks you are her go to person.Seems you dont understand that and thats sad.
I've always been my kids go to for a moan person and I just nod and agree in the appropriate place and NEVER give advice unless specifiaclly asked for .Even then I tell them it might be what I would do but they are under no obligation to do the same .Tell her you're finding the situation difficult but know she's having a bad time and that you'll be there for her and that you'll attempt to keep quiet and things will be fine .

I would absolutely massively suggest you see a counsellor to offload and get some clarity and boundaries

It's hard but she's not you and what you found easy she might not. I worked full time throughout my pregnancy and find it hard that my Daughter in law is struggling so much with everything. No she's not the first person to be pregnant nor the first to struggle with it but the fact is she is. So all you can do is switch off and not take all the complaining to heart. It is what it is so just suck it up and be there for her, your her mum and someone has to be there and in this case it's you. You lucky person you. Seriously time to don your tin hat, make amends and just tell her you know she's having a hard time and tbh it's just as hard for you to stand aside and watch it.

My Dd and DSil work full time and he works long hours, so I have always been very hands-on with helping with their three children.
After saying that, they treat me with the utmost respect and vice versa and if my Dd did tell me of any problems she had, I would be very sympathetic and 100% on her side.
There seems to be quite a few Grans, walking on egg shells with their Dd's and being made the unofficial "whipping boy", for all their woes.
Can you imagine if the shoe were on the other foot and you were being the nasty one. They wouldn't put up with it for one minute.
So that you can still be involved with the Gc, I would make myself scarce as far as your daughter is concerned but continue with the childcare.
If she does insist on you listening to an account of one of her arguments, in future, make non-commital sounds but offer no advice.

You can't dictate the relationship between two adults, namely her and her MIL. I'd suggest taking a HUGE step back and offering just tea and sympathy.

Thanks.To clarify regarding her MIL I have taken a huge step back ,believe me.I have listened but not told her what to do other than even if they can't have a good relationship MIL is also a grandma and it would be sad for her not to have time with the little one.I read of the sorrow of estranged grandparents and feel I'm not the only,or most important grandma despite their differences.And it was her that raised the issue of counselling and I just gently asked if it was still being considered.
But every little thing seems to cause irritation,only the other day she wanted me to go for a dog walk with her and as we parked up I asked really nicely if she wanted me to move her big handbag from the footwell to behind the seats as she was unstrapping DGD and I got my head bitten off. I spent the walk wishing I had never gone,close to tears.
I give up for now in that I need a lot if space from her. I really do.And if that's makes me a bad mother so be it.This has gone on even before she became a mum. And of course I won't withdraw completely,or not help with grandchildren but I do deserve respect.And yes I agree each situation is different,and just because I coped,my DH was consistently helpful and my MIL was lovely.But her sister also gets the hot and cold treatment recently,asked to have the little one only recently for 24 hoursin an emergency,then messages ignored and unanswered because she doesn't feel like talking to anyone and it is 'annoying'.
I sound unsympathetic, but honestly today I just needed to vent.

I think you both need to look at boundaries. Tell your daughter how her comments make you feel and try not to take everything to heart quite so much. One of my daughters can be like this but I only allow things to go so far before saying something. You wouldn't let anyone else treat you like this so why should your daughter ?