I have Borderline Personality Disorder. I don't try to control or manipulate people. If anything, it's my worst enemy because it leaves me open to being used. You can't just look up the description of a label and assume that's how the person is affected.
DH has been hospitalised several times and I never contact his family (on his instructions). Don't assume the DIL is deliberately trying to damage the mother/son relationship. Also, after surgery, your son may be on strong pain killers. These can alter the taker's perceptions and behaviour. DD2 was once given morphine after surgery and it changed her completely. She was rude and totally egocentric. I was constantly apologising to the staff who laughed it off saying she wasn't the worst they'd ever had. Once she came off the morphine she returned to her old self.