Ah TNC - that's exactly why we have this space. Because here our concerns are valid, our kids are awesome and we are heard! *HUGS*
Most schools will say a child is appropriately challenged if they don't see what they "expect" to see from a bored gifted child (ie work done accurately, quickly, and then wondering around the class with nothing to do, an angelic expression on the bemused face and still polite, engaging and asking for more work constantly.)
It's not the reality and unfortunately, especially for EG/PG girls who are usually people pleasers, you need to read the situation and them from early to ensure they don't go underground and just learn to live with it.
One thing you might want to consider is to get some of the higher level montessori equipment for her at home, and then encourage her to speak about it at school, or for yourself to read some of the original Maria Montessori books (many are free on Kindle app) and then enthusiastically share some of your favourite pieces with the directress.
Of course, this is all assuming you think it's worth it in the long run. Otherwise maybe plan B is worth considering too. There is no reason why you cannot homeschool Montessori too - the materials are widely available, there are loads of Montessori homeschooling pages on FB and alternative sites for making your own materials inexpensively too. There are books available et voila!
It's not an easy decision and it's one you and your family will need to make together at some stage based on what your long term plan/outcome goals are for your family
