When Sabina was a kid, she had a hard time controlling her transformations and it was very frightening for her, especially when activites at school* involved shapeshifting... When she's upset it's hard for her to maintain solid form, and she tends to get stuck like this. Ashley can only do so much because she's an ordinary human (with her own fear of bodily transformation), and Leaf is just not a great father the way he burns himself out, which is why he's not around.

It's a really frightening experience when you go through unexpected changes and feelings and you're not at home where your parents can comfort you.

Honestly, Ashley's co-workers** Etrovarian and Tentel (I think those were their names?) are the real MVPs in my head, the way they "advise" / "squawk at" the school on Ashley's behalf so she can look after her daughter.

*they live in a space station full of aliens, I established this in an unrelated story and now I'm sticking with it

**their jobs are that they're ghostbusters, yes that's staying canon too