Maggie can be seen as a symbol representing Roberta and Twyla's mothers. Both are in some way responsible for the girls being brought up in a children's home: Roberta's mom is responsible because she is ill and cannot cope, and Twyla's mom is responsible because she appears to have mental health issues.
The question of whether they actually kicked Maggie is never fully resolved. However, there is no doubt that they wanted to; for Roberta, wanting to do so is the same as doing it. Roberta's own mother was brought up in an institution and the mute, shambling, pathetic figure of Maggie gives her a terrifying glimpse of what might be in store in the future.
Twyla identifies Maggie with her own mother, a childlike creature who lacks the maturity to raise her own daughter. She says how much she wanted to kill her mother, for instance, when she groaned and reapplied her lipstick during an Easter service. Kicking Maggie, whether they actually did it or not, represents a kind of payback for both...
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