The option should be there when shes in your room and cleaning it. Happens at 16:00 almost every day if i remember correctly. There are then 3 options, one to just stare and one to grab her ass. The 3rd one is the HJhow do you get Brenda to give you that HJ in your own room (after unlocking this action with the pool chair HJ)? I cant seem to find a way to trigger it
Edit: just checked, the time is 16:00