That's just it: you don't know what she would have decided. Nobody does.
Mormons believe that baptism by the proper, restored authority of the Holy Priesthood is an unalterable requirement for eternal salvation. It is our goal and mission to make that crucial ordinance available to every single human being ever born.
By performing a vicarious baptism for a deceased person, she is not FORCED into anything, but is given the opportunity to accept it as her own. Without the vicarious baptism, she would not even have that choice.
I wish people would better understand the doctrine and calm down. Nobody is being forced or coerced into anything here. You don't automatically "become Mormon" when a vicarious baptism is performed for you after you die.
Save your energy. Some folks have fixed ideas about Mormons and won’t change those ideas no matter how many facts they are given. Maybe it’s because they don’t like Romney. Who knows. There’s a lot of intolerance in this world. Most of it comes from liberals but some conservatives are that way too.
Kudos, a very plain and calm explanation.