I would like as many females to repond to this as possible...

Im looking at having a 3sum with my g/f and she doesnt want to disguss it much. She has indicated that she will have a 3sum with a friend but i said a stranger would be best as the stranger would come and go without any other folloing contact.
The questions are do i suprise her with a stranger (a nice 5 star hotel room would be the setting) or do i try and convince her to do it with a stranger ? She isnt that open about sex but as i said she agreed to do it with a friend,how many women really think about and want to do a 3sum with 2 guys?????????