I wouldn't be comfortable with religious paraphernalia in a GP office either. Regardless as to whether you miss read it or not, when dealing with people from all walks of life, it's just not the place for it.
As for what was said, it really depends as above if they said somatic or psychosomatic.
DD & I both have POTs as a comorbid condition with both pernicious anaemia & Ehlers Danlos. Neither of us pass out. I've passed out twice & DD a few more times pre getting B12 injections. We never pass out now, but do get dizzy/white out as if we will, but lying down or even sitting & resting if you catch it early enough. Drinking lots of fluid & extra salt helps too.
15 is old enough for a tilt table test, but you'll need a referral to a specialist unit usually attached to heart clinic, as POTs isn't generally understood. We have to travel to the Syncope Clinic in Hammersmith in London.
POTsUK is a good place for information, so GP is right if they recommended that. They have fobbed you off though as yiu need a referral, at very least she needs a correctly done "active stand test" you can do this at home to check fir yourself with a BP monitor too, instructions on POTSUK diagnosis page.
Id suggest looking at the "Beighton Score" in images to see if she's hypermobile at all & ask fir a rheumatologist referral if she is hypermobile.
Id also insist of vitamin B12 blood tests, especially if there's any PA in your family, or if she's vegan/ vegetarian, heavy periods, has had covid,mor may have been messing around with those laughing gas canisters. This can be a cause of POTs & prompt treatment cures it, or if hypermobile too, then at very least it can improve things a lot.
I've a good link for explaining it to teens & school & I'll pop back with it, but she needs an official diagnosis to access treatment & help in school & any underlying causes treat & managed. It can affect much more than just dizziness. Thankfully some teens do just grow out of it & there's no underlying cause bar maybe hormones