What level are your girl's body parts? I lowered the level of the clients so they might just be too high of a level for you to notice an exp increase.
Between 20 and 40, depending on their "role" they have to play in the team (a 26-21-22-39 for the anal freaks, a 25-19-35-22 for regular use, a 23-36-26-26 for boob jobs, etc.). Girls are level 26-27 in the main game (had to restart, so they could be better...). I checked the game export / inport data and found out, that XP grows, but only by a very small number.... so I can not see the bar moving if "+12" is added to a sum of 26000XP e.g. Dont know if this is okay....