We have been doing this forever (9 years), so it's simply part of the ebb and flow of the year. In January, I start mentioning to our AP that I will be in matching soon - using comments like "Can you believe it's been a year already since we met you?" Once I have narrowed down a candidate for skyping, I tell AP something about him. This year, the incoming AP is from the same country as current AP, so I made sure to tell current AP that we were especially excited about this. AP came home in the middle of my first skype call with the prospective AP, and I invited him to come say hi. I made sure to tell them they could talk in German and walked away. After another week or so, once I had skyped with the prospective AP several times, I asked current AP if he would be willing to skype with prospective and talk him through the schedule. After that, I put prospective in touch with 2-3 previous APs and then he skyped with the children as well, and we matched. By then, incoming AP was already FB friends with current AP and two former APs, not to mention DH and me. We're a big happy FB network.
Through the whole matching process, I make sure to tell current AP how great he has been so that he doesn't feel like he is being replaced. He knew we loved last year's AP as well so he also knows that it's possible to be very excited about someone new while at the same time enjoying and appreciating the current. Our AP from last year is coming to visit for 10 days in a few weeks, and the two APs are FB friends from last year's matching process and I'm sure will be fast friends once our former AP is here. I do my best to make sure that the current, previous, and incoming APs all understand the cyclical nature of hosting and how much each is important to us, no matter where they are in their cycle, so no one feels that he is being "replaced" or, conversely, that just because we love the current one we won't love the incoming as much.
I think it's great to be sensitive about your current AP's feelings and also to include her, if you trust her judgment and if you want her to represent your job and family to the new AP. I also think it's fine for you not to include if there are things you want to change. WIth one AP, we asked her not to talk about her use of the car with the future AP because we wanted to change our car policy. I think it's fine to do this - just be clear with the current AP what you're doing.