Yeah, the hair thing didn’t seem to make sense really. It felt like one of those things that are assumed. Rapunzel has long hair, that is known, so they didn’t feel the need to justify why she had long hair even though they should. The cartoon movie does. I am not sure what the justification in other Rapunzel stories are for her having long hair though. I have not seen many versions of that.
I think she just used her hair as a rope. She could have tied sheets together if that was all the purpose it served.