Erin dates Joey in "The One With Ross' Library Book". She meets Rachel the morning after she and Joey have slept together and Rachel ends up liking her so much they spend the whole day together. Rachel and Phoebe think that "cupid" brought Erin there to be Joey's girlfriend and encourage Joey to seriously date her.
Erin speaks four languages, is a Mets fan, drinks beer at lunch, and likes sandwiches. At first she seems to really like Joey, but after dating him a couple more times she disappoints Rachel and Phoebe by telling them that there's "no spark."