Talk

You have two choices I think. Either use this to your advantage, or nip it in the bud now.

You don't mention hometime. Do you pick up then? and does MIL come with you?

Have you asked her to stop coming in the morning.

YANBU, but she isn't a mind reader.

She is probably trying to be helpful and no doubt enjoys seeing her DGD every morning. But it's bothering you (and I can see why given the situation with your DD1) so could you have a gentle chat with her about it? Or maybe suggest that she takes DD2 to school one day per week on her own and you will do the rest?

Could she be persuaded to pick her up from school and drop her home instead?

This is akin to having someone coming round to wind the children up in the afternoon, just before supper, or just before bed. It's fine to explain that it's a stressful time of day and not convenient. It's also fine to say you miss the time alone with DD2.

Would you consider offering her pick ups? Or asking her to do the school walks run one day a week?

She sounds like she's a granny who wants to be involved.

Maybe she thinks she's being helpful, or really misses or looks forward to doing that with her dgc. Maybe she misses doing it with her dc..

Maybe have a quiet chat with her and say that you miss doing it with dd on your own and the quality time and that you find yourself stressed at that time in the morning. And if she's really gutted maybe you could arrange to do them on your own, but for her to come round and drop dd off on her own one morning a week or something.
You could put your feet up with a cuppa.. and enjoy the rest of the mornings alone with dd.

Could you give her a day when she can come. Say something like "it's been lovely having you walk to school with us. Let's make this a regular thing every Friday?"

Could say it's an end of week treat for dd and makes it more special being only one day?

This would annoy me too. It's so intrusive. But, a simple "I think I'd like to do the school run alone from now on" will fix it!

YANBU at all. She'll probably start following you to the toilet next

Although if she's that bored, as others have said give her a day to do it by herself while you get an extra hour in your jimjams.

I am with Nunk don't beat around the bush.

This would annoy me too, could you leave a bit earlier or walk a different route?

Wow, what a cow - wanting to regularly see the grandchildren and giving them hugs...... Nightmare.

OK, seriously, it might be annoying how regular a thing this has become, but talk to her about it and cut it down a bit if it's that disruptive. Alternatively, be grateful she's bothered.

I'm with uncle t. I wouldn't be rude or passive aggressive about it, it's lovely she's trying to share it with you and however annoying you may find it she might just see it as an opportunity to bond with you both.
Don't cut off your nose to spite your face as they say, she's clearly game to help out and be hands on and you never know when you might need that in the future!

YANBU. That's intrusive. Intentions are good but definitely too involved everyday!

Yes, you need to say something. My MIL is similar and always wants to pick up the dc, whereas if we can, we would like to pick up our children.

Oh dear! Every day is a bit much. I think you are going to have to tell her it's your special time with DD and you don't want to share it. Can you ask her to take DD one day a week without you so you can do something else go back to bed?