My prayer is that even though her newfound attention for the kids appears to be manipulative from yours and my point of view(as well as masking some of her own issues as pointed out by ford), that it might make an impression on her how much fun it is to be with her kids and what blessings they really are.
FIB, you have been there for your kids and they know that. They want to enjoy the company of BOTH of you, and deserve that as well. This can be an incredibly tough pill to swallow when we as adults anticipate motivations behind the scenes that are less than admirable. I want to offer you the perspective of celebrating the fact that, if maybe only for a short time period, your kids get to have the mom THEY deserved all along.
Again, my prayer is that what would start out as manipulative would grow into a fondness that endures.
