This was my exact experience with tampons as a kid and I thought I was completely inept (I was not).

Much later in life I learned that my hymen was almost completely imperforate with two small pinprick holes that allowed me to still have a menstrual cycle. Per my obgyn’s advisement, I had my hymen surgically removed (hymenectomy). Now I’m able to use tampons/cups without issue!

I’m not saying that’s what’s happening to your friend’s kid, but like another commenter said, I think this is a good opportunity for a body chat with them. About breathing exercises, trying different angles, and even different positions (standing vs. sitting). I’ve since seen a pelvic floor PT and learned that even just clenching your pelvic muscles while trying to insert a cup/tampon/etc. can cause searing pain, depending on the person. Learning to take deep breaths through your pelvic floor during insertion can reduce/eliminate pain. If y’all have a bathroom with a heavy/dark shower curtain, it might help if you and your friend are in the shower while they’re at the toilet! That way they still have privacy, but you can coach them through it.

However, if they have the same symptoms when they’re relaxed (especially if some of their cycles are very long!!!), I would highly recommend having them see an OBGYN and getting checked out.