I have also been considering MMR for my teenage daughter. I even asked the pediatrician, who has exempted her from further vaccination due to previous reactions to other vaccines, what he recommend.
He did not think she needed it, which surprised me.
He said that, first of all, since she was in part-time day care from age 3 months, he is sure she would have been exposed from all the other infants and children, who got the MMR and then shed live virus cells for the next 3 weeks. That is apparently how, in part, live virus vaccines are supposed to work.
And secondly, the MMR risks risks for post-pubertal females include a whopping 25% who get arthritis/arthralgia. It's listed on Merck's website, and on the package insert.
You know, you can always get titers done, where they check for antibodies to determine whether you are already immune--which would complete tell negate any argument for getting the vaccine.
Our ped did suggest checking titers for rubella when she's older, well before she considers pregnancy.