Cooking easy freeze and re-heat meals that she can eat one-handed as she won't have time for cooking.

Arrange to take her oldest child out with your DD a couple of times a week even for an hour so she has some break times.

Get her a big whiteboard with textas so that she can write notes and organise herself eg. writing when each twin fed, slept etc so she can keep track.

Offer to mind the twins for 15 min each day so that she can have a shower.

Tahnt's all I can think of at the moment.