Here's my guess as to what Stella's past is.

it's not really a guess cause it's really obvious.

I'm assuming that her parents just didn't like her and viewed her as just a baby maker or something, so they gave her whatever she wanted in order to shut her up. Basically rewarding her bad behavior, therefore enabling it.

how surprising. The reason Stella acts like a spoiled brat is because she's a spoiled brat. who could have seen that coming?