There are some misconceptions here. Pan means being attracted to anyone, not everyone! Just as bisexual doesn't mean you fancy all men and women. A straight woman is saying they fancy men, but it doesn't mean they fancy all men - there's a huge difference between Tom Hardy and Arnold the eighty year old weirdo next door with BO.
By pan people fancying anyone - it simply means male, female, non-binary people, fluid people, trans people... I guess think of it as bi but not ruling out someone because they're trans etc (though some pan people may also be specifically attracted to trans, enby people etc).
These things are fluid, especially in girls/women. She's also very young and starting to explore feelings and attraction. All you need to do at this point is reassure her that you love her whatever and she's always welcome to come and talk things over with you.
Depending on the school, area etc, things are really different in many schools now, with children being very aware of and welcoming of non-binary, fluid, trans, bi, gay classmates. My DC don't bat an eyelid that there are some trans kids in their primary schools. My hairdresser's kids are at a secondary school in a traditionally less 'naice/liberal' part of city and she says attitudes to LGBT+ kids are very similar - open and accepting.
Labelling makes some people uncomfortable, and others comfortable that they've finally found something that makes sense to them, and makes them feel less 'other'.