I don't find Maya to be very mature she very native about how the world works even for her age. Josy actually solves issues Maya doesn't. Maya because of what patrick did to her excepts people to leave but that isn't the same thing as being mature
Yes, she is naive and gullible and not that bright when it comes to being street-smart, however, compare to Josy, she doesn't seem like she is depended on others. She doesn't seek other people's attention / validation or approval. As far as I've seen, she has a goal to achive, something that she really wants to do and that's to help people in need.
Josy on the other hand thinks too much about what other people say about her and this very situation kind of force her to pursue modelling / talking about fashing because someone irrelavant told her she is '' basic ''. I don't think she is a basic character, she is just conflicted, trying to find her place but letting her emotions getting the best of her, letting her emotions control her actions is not smart / mature.
TLDR : Maya is emotionally more mature than Josy.
Josy is smarter / aware of her surroundings and can pick up things that Maya can't. She is kind of street-smart.