SOLVED. Older children's chapter book about mom that won't leave

[Rampion]

I'm hoping you could help me find a book I've been looking for! This was a book I read when I was around 8 (would've been 2008-2009ish), maybe? I got a box of books from someone around that time that were hand me downs from someone, so they were older titles. This book in particular was from either the 80s or 90s, though I don't remember which. It was probably around 100-150 pages, and was a chapter book. Anyway, the book was about a kid (don't remember the gender, though I'm leaning towards female) who lived in an apartment with their mom. I don't recall if there were any siblings or not. I feel like either the main kid or their best friend had a little brother. The main kid was probably somewhere around 10-13, so, middle school aged. So, the main point of the story was that the main kid's mom refused to leave their apartment. So, because they also didn't have a dad (not that I remember, I think he had maybe passed away), the kid had to run all of the errands for their mom and everything. The mom hadn't left their apartment in years. If I remember right, I think she had said something along the lines of that it was so hard to get up the stairs, she was never coming down again. So, by the end of the book, the kid decides to spend the night in the library (I think, they stayed somewhere, and I think it was the library) without telling their mom, in the hopes that she'll decide to leave to look for them. I also remember a random scene where the main kid is sitting with their best friend (who I wanna say was male) on or near a bridge. They are both playing cards together, and talking. One of the cards then slips out of their hand into the water below. As far as the cover goes, I don't remember, but I think there were kids (mc and best friend, most likely), and I strangely feel like there's a bike on the cover too. Otherwise, I don't remember the cover. I don't remember much else, but hopefully that's enough to go by!

[Rampion]

I found it elsewhere! It's The Law of Gravity!

[Rainbowheart]

Glad you found it!

Also known by the title What Goes Up Must Come Down.

[Rampion]

Oh, okay! I didn't know it had another title! Thanks!