I'm with annie on this one. I think your friend would be better off having the baby and letting her sister adopt it. But before she makes ANY decisions, she needs to speak with a well informed adult about the risks, consequences and procedures for all of her options: Keeping the baby, aborting it or adoption. This way she can make an educated choice that will benefit everyone involved.
Thank-you for your very informed answer on yahoo we just got people saying we were stupid and that it was impossible.
No, not once the embryo has implanted and begun. The only time gestational surrogacy works is in the first five days after the sperm meets the egg. Up to that time, it is a round embryo in a protective "shell" and can float free. After that point, the shell breaks open, and if the embryo does not attach to the uterine wall by blood vessels it will die. And it has to stay attached from then on in order to keep living. Once the embryo begins to grow, it is attached to the uterus by blood vessels and a placenta, and that is all too complex and delicate for an embryo to survive being removed at that point. Besides, her sister would not have a placenta waiting.
This is a lot like the question of whether an ectopic pregnancy can be moved out of the tube and into the uterus without loss of the embryo. Answer to that one is also no.
If your friend wants her sister to have the baby, the only way she could do it is carry to term and then have her sister adopt.