Continuity mistake: In the beginning when Deadpool is in the front seat of the cab, the passenger window is rolled half way down, although it seems to change during the scene. But then, when he pulls back his mask, the window is now rolled all the way up.
Continuity mistake: When Deadpool comes back to the duplex after cutting off his own hand, he grabs a red towel off a Chevy Citation parked outside. When he enters and flops onto the floor, the towel is yellow.
Answer: Yes that would be how she most likely was able to tell.