In the mid- 90s we had a college student come to my class for a project on the impact of sci-fi/fantasy novels on kids. We had a selection of books to choose from, like “Girl with the Silver Eyes” and the Tripod trilogy. There was one I started, but had to give back the next day as the project ended earlier for some reason.
I think the title had something to do with “moon” or had the word “moon” in it. It started with a girl escaping a city through the sewer (I think she lived there with extended family?) to go find her mother. I think it was kind-of in the dystopian genre. The mom was presumed dead, or shunned from society in some way.