Oh man, I totally feel you on this! I went through something similar when my cousin was trying to find her old dance Instagram that she'd forgotten the password to. We spent forever clicking through these janky viewer sites that either wanted us to download something sketchy or just showed loading screens forever.
What ended up working for me was this site called https://viewverio.com/dolphinradar/ that my roommate uses for her social media stuff. It's not perfect but way more reliable than the random ones on Google. The interface is straightforward and it actually loads instead of giving you those fake "processing" bars that never finish lol.
My cousin ended up finding her old account and we could see all her posts from 2019 which was hilarious because her choreography style was SO different back then. The whole thing took maybe 10 minutes once we switched over. Hope your friend finds her fitness page!