Cindy adored Caylee. She just had reached a point in her life when she expected not to be starting all over again with another baby. The 'not enough money,' I believe, refers more to the inability to pay the legal expenses associated with a custody petition. I believe that, despite her plans for retirement (plans that fell off the horizon years ago, given the family's financial situation), she would have happily taken custody--if it weren't for the difficulties a continuing relationship with Casey would present.
It's just a very, very difficult situation. Cindy knew Casey was a freeloader. She knew she was a liar. But I just can't believe she knew she was capable of doing what has been done. She muddled through a rough situation the best she could, caring for Caylee when she had her, despite her sheer exhaustion from bearing the full weight of this family for going on two decades.
I have a family member who did this, as well: my father, a sociopath. I learned of this only after moving out of state; when my family and I visited "home," we stayed at their house, and my father did not conceal this from me. He'd wait until about an hour before my mother--who supported the family (including a grandchild who was the product of a "hidden" --read that: unacknowledged--pregnancy) since I was a young teen--was due home from work, then bathe and dress for "work." He would then leave the house until about a half-hour after my mother came home, pretending he'd been at work all day. When she had days off, he either pretended he could also take off (he was in "real estate"), or spend the day at the library, or shopping, or otherwise amusing himself.
There was no income coming in, obviously. Being in "real estate," this could be explained, at least partially, by the market. But my mother at least knew he was lousy as a realtor! They'd fight about it, she'd threaten to divorce him---and she never did. She didn't want him to get any share of the house (which her parents had paid for) or any of her money. (In reality, he'd have no claim to that; it was inheritance.)
Sound at all familiar?