I think you could get away with
Hermione Rose.
Rose isn't exactly a major character and since
Rose is such a common middle name, people probably wouldn't notice (I didn't!).
Also I think steph_brown meant that her favourite name is
Harry, so she couldn't use
Hermione as well. Just missed out a comma, which confused me for a sec as well. But if you read it back with a comma between
Harry,
Hermione, it makes more sense :)