I think you idiots are overthinking things. It's obvious that the reason why she goes for younger guys (total coincidence) is such a turn on for her stems from the way her mother's death affected her. She was already a bit looney before but that event made her develop some fucked up twisted sense of nurturing and care giving. Hence why she rejects and resents being taken care of and instead gets off to behaving like an actual mother that their bfs get to fuck: paying for their stuff, taking them in into her house, the whole 9 yards. She justifies it as just being a good partner but absolutely nothing she does indicates that. Her desperation also comes into play. She has self esteem issues and this makes her feel somewhat valuable. But she knows it's advantage taking, the guys she bangs know they are taking advantage of her "generosity", but it's a non spoken agreement in which they feed off each others fucked up : one gets sex and access to her money and resources, she gets to feel useful and a semblant of the motherly love she was deprived of. 
Thank you for coming to my TED talk.