Is the split session due to necessity? If not, I would just make it a regular session.
I think ET (extensive tempo?) can have a minor benefit for keeping weight in check
Interval work…I think one of the official answers for that is that it ‘helps with rhythm’. I have heard explanations for it before but I partially deleted them from my brain.
For weight gain issues I would just increase the low intensity general work as much as necessary. That being said, poor eating habits can overcome any training effect when it comes to bodyweight.
Another thought, does she need to do presses? I have cut heavy upper body stuff way down in my program (for girls) and don’t miss it at all.