They are so different that this has to be about what she wants. Is she looking for small, focused, disciplined, intense? That’s Banneker. Is she looking for big, lots of independence, lots of activities/ECs? That’s JR.
Also worth looking at course offerings; if she wants to take lots of APs, JR offers about 30. Not sure if Banneker is able to offer the same range given the smaller size.
Location is also a question worth considering: if you’re very close to one school, that makes a difference in terms of how long of a day she’ll have.
I assume access to JR means that you’re in-bounds or coming from an in-bounds MS, meaning maybe she has a lot of friends going there? Could that be why she’s so torn, meaning she really wants the Banneker environment but also wants to be with friends? Is she coming from Deal and didn’t like it because it’s so big and overwhelming? That’s worth teasing out; if she was unhappy in Deal’s environment and/or wants small and intense, she will not get that at JR and could end up pretty unhappy academically.
Ultimately, if she’s really torn (and you’re in-bounds for JR), she should probably try Banneker for 9th since she can always switch back to JR if she doesn’t like it.
Good luck!