Hi taylor!
I don't know which admin sorted your sheet so maybe they can explain better, but as a reader I don't really get why her mom would leave Hogwarts, especially after one day. I imagine that all muggle born students are fearful of the magic in some aspects because they never really knew it existed before and I'm sure, at age 11, it all comes as a bit of a shock.
That said, I personally find it unlikely that Brynn's mom would just be allowed to leave Hogwarts after complaining to the headmaster/mistress. I believe it is mentioned in the books that part of even going to Hogwarts is learning how to control their magic, otherwise I imagine it builds up in them and explodes randomly---Harry breaking the glass of the snake enclosure, Aunt Marge blowing up, for examples. This means Brynn's mom would be having random explosions of magic because she's never learned to control it. I don't think she could just pack up her wizarding stuff and forget about it, like you have mentioned in Brynn's sheet.
If I were you, I would either find a way to more plausibly explain Brynn's mom leaving Hogwarts and how she dealt with her magical abilities through out her life, or just scrap the idea completely. Personally, I would just change her leaving Hogwarts, because that seems a little too unlikely and it'll be less to explain. You can still have Brynn's dad as a Muggle however--maybe they were childhood friends in the same neighborhood, or met through some of the mom's muggle friends.
Let me know if this helps or if you need someone to bounce ideas around with!
-Aisling