What is up with her, what is her problem?

Situation is: Daughter has teenaged sons. Good boys. She spends noooooo time at all with them. I mean it has been months since she's spent a full day with them. She's just as happy as a clam, going to this party, that event, this and that, hanging out with this friend, going to that friend's house when she's not at work. The boyfriend's at her house all the time. Seems the gatekeeper has opened the gate, let the boyfriend, his friends and family in, and her own children out. The boys are at my house so they're safe and my husband and I enjoy having them around. They don't seem to care what she does as long as she doesn't drag them around with her or include them. I seem to be the only one who is baffled by this behavior. No one else seems to care or they just dismiss it and her as not having good sense or something. I just can't for the life of me figure this one out. Can't wrap my head around something like this. What is going on? Reminds me of the mother in the movie "Flowers in the Attic" who didn't care anything anymore about her kids. Just moved on with her life. What kind of stuff is this? Honest and frank answers are welcomed.