A writing teacher once told me that you should resist including flashbacks in your fiction at all costs. If you absolutely must add a flashback, each one can be no more than three lines (or was it sentences? Lines, probably, because with sentences you could cheat, spinning out subordinate clauses for pages, sprinkling liberally with commas and semicolons).
The reason for this perhaps extreme prohibition is that flashbacks can lead to a static narrative in the story's present. The reader can almost picture the character sitting on a couch in a dim waiting room, tapping her foot as you methodically plod through all the steps that got her to this point in the story. Perhaps worse, because you know you need to get back to the present, and rescue your character from that waiting room where she's growing more sullen and uncooperative by the minute, the flashback can fall into a weird neither-nor land: not quite summary, not quite scene. Especially if the flashback seems to you to have a primarily explanatory function--how did Suzy get to be so sensitive about her appearance?--you're especially likely to fall into this mode.
I find that in my own writing process, the early stages of a novel tend to be full of flashbacks. Probably even more flashback than present narrative. What that tells me is that I've either set the story at the wrong period in the character's life, or that I need to give some of these experiences to other characters. I have to find some way to get these flashbacks into the main story. Either that or I'll have to come up with some kind of lovely, stylistic move to weave memory itself into the story, without making the story about a person being struck by random flashbacks over the course of an otherwise ordinary day, or week, or ... OK, in the right hands, I can see that being a very good story.
In this case, though, I think I'm going to hand off some of these experiences to the other characters. Because that's the other thing I find that I do in the early stages--create a bunch of characters, and then not give most of them enough to do. So instead of having the mother's experience at her school be a flashback, I'll have it be her daughter's experience in the story.
More thoughts on flashbacks: the lack of them in the Odyssey (per Auerbach), and as a function of point of view.