Quoting ~Cullen's Mommy~:" Should I worry about her spitting the milk back out? Yesterday she did it twice that I actually saw ... [snip!] ... I actually saw and then 2 other times when she was done and I pulled her away I noticed my shirt below my breast was soaked. "
Nah she's probably just comfort nursing or eating to build your supply but may not actually be hungry, so she spits it back up. I'd only be worried if she did it a lot, like at every feed.
DS did it a few times but he stopped when he stopping nursing to much.