After talking things over with Wolverine and fellow X-Men member Dagger, Cyclops sent out Domino to invite Deadpool into the X-Men, however Deadpool believed Domino was sent to kill him. They fought and Domino later tied Wade up on a bed in order to keep him safe. Later, she overheard Wolverine and Cyclops talking about Deadpool and thought they did want to kill him because Wade was trying to kill Ellis Kincaid, the father of X-Men member Mercury. However, Cyclops merely wanted to send Deadpool on a special mission to China but now Deadpool was on the loose again. Deadpool then went on top of a building about to kill Ellis Kincaid, but was stopped by the X-Men. Moments later Wolverine had realized that Deadpool didn't plan to actually kill Kincaid but to make the X-Men look like heroes to the citizens by defeating him.
Geeks should probably note, when Domino first appeared in the comics it was not Domino at all, but my girlfriend Copycat.
Domino and Deadpool met in the following comics:
Deadpool (volume 3) #16-17