I thought the maximum you could take was 4 HLs- that how it is at my D’s school. There was still grade inflation at her school, even in the IB- not everything is sent off to the IB so there are internal grades that can be inflated. Plus the AP also has rubrics which they have to use to grade all the non multiple choice. Usually, the IB kids still end up at the top percentage of class rank, since all of their classes are weighted including TOK.
I would say that 4 HLs is more difficult senior year because they will have 4 IAs on top of the extended essay. Most of our kids supplemented their IB senior year with AP classes.
Unfortunately for your daughter, it’s a new program. It could be a feeling out process and her grades could suffer.