Considering that Meredith thought her name was "Holly" when Thatcher needed a liver transplant, I'd say it's fairly obvious that she has no interest in pursuing any sort of family relationship with Molly.

I feel like Lexie only managed to break through Meredith's considerable emotional walls by being persistent and proximal. She was always there and was an extremely likable person that even Meredith couldn't push away forever, despite her best efforts and natural proclivity to do so. I don't think Maggie has managed to ingratiate herself the way Lexie did.

I always wonder about her but we already saw enough of Meredith's sisters so better this way.