Should my GF be in her best friends pic as planned?

My GF is a very ual, sensual girl. I love it because the flame never dies. Her childhood best friend and fiance are having an photo session done this weekend. She has chosen to have a series in the shoot that includes a second female. She chose my GF because of the close relationship she and he share with her. I dont get worried about her with them, but this is nagging me. My GF and her friend have already purchased very y lingerie. Her friends fiance supposedly has very large manhood and part of the set is having the two girls handle it while he is erect. she seems even excited to see it. (wish i could be so lucky) She doesnt have to perform anything on it. He then will complete his part on them in various locations. they both got very tan and are wearing black for full effect of that part. geesh. they have the entire session planned and ready. Should i let it go, not worry and relax. shes not worried about pics getting out because there are already. but, i think that he will complete on them or her in some way is just making me feel bad? i hope he focuses on his fiancee. i dont think i am going to ask her to not do it. they have known each other longer than ive known her. any ideas on what i can say, or suggest? a change i can recommend that doesnt ruin it for them, but puts me at ease? maybe i would be as open as they are if i were around that long. i guess not stopping it completely, but minor adjustments. hope to hear some great feedback. thanks!