Do you know 1). If the right to choose means "the woman with the baby in her womb" -- (a gestational surrogate) -- who has no genetic connection to the baby because an implanted embryo is used, has more legal rights than the parents of the implanted embryo?
Your question is subjective. More legal rights? It depends on which rights you are talking about. The bottom line here is that under California law, no one can compel a pregnant individual to have an abortion.
2). Can the surrogate break a contract because she's pregnant, as per the terms of the contract?
It depends on what the contract says.
In a typical surrogate contract, the surrogate for an agreed upon sum accepts being impregnated with an implanted embryo and agrees to nurture the baby to term, at which point the surrogate surrenders the baby to the embryo providers. Apparently, this particular contract had a clause which compelled the surrogate to have an abortion at the whim of the providers if there were any test results projecting an unsatisfactory outcome of the pregnancy. The surrogate agreed to the clause. However, California law would negate that clause in that a pregnant person cannot be compelled to abort a baby.
The surrogate in this case refused to abort (which is her legal right). Now whether that nullifies the contract is wholly dependent on how the contract was written. But this case is now complicated further because the surrogate has fled the State and has now given birth in Texas where its laws grant legal protection to the person giving birth. I would assume that her decision to leave California was a breech of the surrogate contract. If the contract was tightly written, then there would be civil contingencies for such an action.
This is essentially a contract law case, with the exception that one of the stipulations of the contract was not legally enforceable.