What Kristina told Ava was that if she was called to testify the truth about Sonny, when she would also testify the truth about Ava. It was an understandable point to make and there was no reason to think she would be physically attacked - and she wasn't. It was an accident.
Kristina is far from perfect, but she was not careless during the pregnancy. Molly and TJ knew Sonny was Kristina's father. If they considered that to be an issue, they should have let Kristina know she was to stay away from her father during her pregnancy and Kristina could have agreed or changed her mind about being their surrogate.
Karen L.