Is what my friend claims true, that she has a Muslim jinn who helps her do good deeds, such as exposing sorcery and treating demonic possession, and does this not contradict Sharia, and is it permissible for me to ask her if there is sorcery affecting me or to ask for her help in getting rid of it without charge?

The woman is either a liar, in which case she must be avoided, or truthful, in which case she must also be avoided, because seeking help from Jinn is not permissible under any circumstances, according to the preponderant opinion. Therefore, it is not permissible to seek help from that woman or to ask her about anything from the unseen under any circumstances. What is obligatory is to advise her and call her to repentance.