You need to decide what you are going to allow, and what you aren't. Then stick to it.
In all honesty, even if your daughter grows up to be the most perfect person the world has ever seen, your MIL is not the type to accept that and stop criticising.
Her criticism has nothing whatsoever to do with other people's lack of perfection, it's the way she is deep inside that drives it.
So - your DP still wants to see her. She's his mother, it's hard for anyone to give up trying, no matter how little hope they have that she will ever be what he would hope for.
But that doesn't automatically mean that you or your daughter need to see her. If you do see her, then it can be on your terms, not hers.
If you think DP will be a pushover, because he's had many years of this and hasn't yet found a way to completely resist it, then you maybe need to say that he shouldn't take dd to see her without you, and that you will only go on X conditions, for X amount of time, etc. Or that you won't go at all.
Grandparents (and other family) have no automatic 'right' to have their grandchild left with them, or to see them at all, if they behave this way.