Hey baby we should meet ill show you a, good time;p
To borrow excellent ideas: She should skype often. (facetime, duo, whatever) and make what time she can to be near them. She moved 4 hours away, and I could guess that on some level the kids really resent that. Hopefully they will get it if she does things like The Duchess suggested and comes to them rather than requiring a road trip. Even if it's for 1 week out of the 6, it might help.