One of my theories is sort of close to yours. Men who abuse are dangerous, often to both kids and mom. Women who are abused are at a much higher likelihood of being murdered when pregnant or have just had babies; abuse can intensify around that time. Women often stay with/defend their abusers, love them deeply, and hope they will change. What I wondered is if the friend was starting to separate herself emotionally from the infant's father. Maybe even starting to allow herself to believe the medical experts' opinions. What if DS was supportive -- not involved as in "going to testify" but involved in helping her friend get strong and independent of her relationship. Boy, wouldn't that be a threat to an abusive partner? Might make an abuser want to retaliate, hurt his partner, scare her. What could be more hurtful or scary than your best friend disappearing? First your baby, next your friend. All just a theory.
At the press conference, her mom used two phrases that I thought were interesting -- "meet with her friend" was one, the other was "adventure with her friend." I don't know if either of those mean anything, but both stood out to me.