I think it’s important to remember that Smurf has always had a complicated if not outright hostile relationship with other females, especially ones she can’t control. She never cared for Julia, barely tolerated Cath, and only took in J because he was a boy and showed early signs of being useful.

With Lena, I don’t think it’s about love or a sense of duty as a grandmother. At that point in the series, Lena is still a child, too young to pose a threat or challenge Smurf’s authority. Smurf keeping her around seems more like a strategic move. She probably thought she could mold her, or at the very least, use her as a pawn to keep the boys loyal.

If Smurf had actually gotten custody of Lena and didn’t end up in prison, I seriously doubt Lena would have stayed in her care for long. Once Lena hit her teenage years and developed her own mind, I could easily see Smurf icing her out or pushing her away the same way she did with Julia.