She is young. Most of us are diagnosed later in life. I was diagnosed at 69 after having an elevated, but stable platelet level since 2018. The biopsy will help the doctor determine whether she has ET or one of the other MPN diseases. They learn a lot from the appearance of the marrow samples. This is a rare disease, see a specialist if you can because GPs and even a hematologist without experience with the disease may not be that helpful. Also, the doctors can be dismissive about the symptoms once the blood counts are in acceptable ranges. The symptoms can be hard to live with. Different treatments can impact symptoms differently and you need to advocate for changes in treatment that impact symptoms too. Finally, hydroxides, or HU, is the first line treatment for ET. However, not for people who are of child bearing age. There are good patient platforms where patients share information, including some Facebook pages. One out of three UK is particularly good. Sorry, I cannot recall the name. The sites all seem to have similar names. Just search MPN and you will turn up more info. Glad she is getting bone marrow biopsy. That is a first step. Also ask for NGS genetic analysis. This screens for a whole bunch of mutations beside the JAK. It is good to have this information.