Well, she could go back to the AP track, but when you pick IB you agree to that grading system.
My daughter looked at an IB program, and we didn’t like the IB rules or how the program was run so picked a different school. We see students ask all the time “Should I go to the school where I’ll be valedictorian or where I’ll be more challenged?”
If the program is new, you could ask the administration how they will deal with this issue and it may be they haven’t thought of it or they might have an answer for you.