can Feliway work in reverse?

Since we've introduced our cat to our roommate & her cat, she's been very aggressive toward them. She'll hiss, growl, & lunge at our roommate even when her cat is not in the room & she'll do the same to her cat. My roommate's vet said that we should just try re-homing them again, but it's difficult to do it properly because our schedules are different. This past weekend we went out & bought a Feliway diffuser to see if that would help. At first our cat's behavior seemed a little more frisky, but it didn't do anything to stop the hissing & growling. Now, our roommate's cat that at first didn't seem to react at all to it, is now hissing whenever she is in the living room even if neither our cat, or my husband & I are there. Could this be the Feliway? Or is she just expressing her displeasure in our cat, but for prefers to do it when our cat's not around? Before we got it, our roommate's cat never really reacted like this to our cat. She was always at a safe distance from her & near her meowmy. This is beginning to cause some serious stress (& possibly strife) between us all. It's a small 2 bedroom with my husband & I & our roommate & her cat.