I’ve been in a similar situation.
Your daughter loves her school as it is now but progressively her friends will move away (or be creamed off to selective schools).
The new school is probably better resourced, with a higher proportion of effective teachers, motivated parents and hardworking kids.
She’ll make new friends very quickly and have a chance to be with the same group as she grows up (and you DO have a fallback if it doesn’t work).
Those saying differently probably have family money and connections to help their kids along (and funds ect. for tutoring, holidays, books, computers and educational experiences).
Lots are pointing out the worst case re: friends and pressure but excellent schools worldwide are packed with kids who aren’t nervous wrecks with no friends.
The alternative (likely) scenario is that she’s treasured for her intelligence at the new school, is given opportunities for enrichment and growth, makes like minded friends, does brilliantly and earns a fantastic education which will serve her whole life.