It's just a poor strategy. He wants to discredit Demarte on the things she said and used to diagnose Jodi. Can't have the jury thinking she is overly attached and clingy because then they will think that's how she was with Travis and they need the jury to think she was the victim in that relationship and all her relationships. They want you to accept some of what she's saying about BPDs, like feeling neglected and invalidated, abused as child, suicidal, but the rest is hogwash. Demarte diagnosed her because of her behavior and symptoms, not what her childhood was like. They want it both ways. If they had gone all in with this BPD diagnosis it would have been better instead of trying to paint her as the victim all the time and trash Travis.
It may not matter anyway. Demarte is doing a good job of generating sympathy for her, which isn't a bad thing. She's just being honest. But if she avoids death it won't be because of anything the defense did.