from my/our experience I would say you should just do as she asks, try it and see how it goes. You may find you like pleasing him and she will love you all the more for doing something she requested. She finds it exciting so the sex with him will most likely be more exciting to watch and enjoy and eventually that will translate to better sex with you as well. I have done this for my wife and her lover and also had it done to me while I was playing the bull role for a couple. Being on both sides of it I can tell you it's hot and once you do it you will want to repeat it. You might tell them no recording if that makes you uncomfortable though and they should respect that.