doesn't look like she does, infact they were trying to hide it from her...that's why as soon as they realized she is on her way back...they got dressed up and stopped fooling around, 2 minutes later Anna walks into the apartment.
Petra gave Alex a BJ and almost started fucking in the living room while Nelly was helping them by locking the door and making sure Anna doesn't walk into the apartment..while she stood there and watched them so fucked up lol.