“Manager” wants to claim ownership over a song they didn’t write or produce. Please help!

I’m a singer/songwriter (I am a 17 year old girl, by the way). I am in Florida, but the songwriting process happened in Nevada. Everyone involved except for me and the producer (who is in Panama) lives in Nevada. Recently I co-wrote a song with another artist (But the song is entirely sung by me). We agreed to split any profit from the song 50/50 (no formal legal paperwork yet). We happened to share a connection with a lady who claimed to be my manager (despite us never having a formal agreement for her to take on this role in my career, this info will become relevant later).

         We recorded my vocals on the song and edited them. We then found a producer who would formally produce a backing track of the song (the original beat used was from a YouTube video so we need a new background track for the song). The producer charged 400 for the backing track, and my family agreed to assume 100 percent of the fee. The “manager” decided to pay half of the price without our consent and has withheld the original mp3 file of the song from us. All we have gotten from her is a Whatsapp message with the song, but there’s no way to transfer that to a computer. Since she is not formally my manager at all, and didn’t assume the entire cost of production, I don’t think she has a right to withhold the song from my mother and I.

        She also claims that since she paid half the production costs — again, without our consent; she told us AFTER the fact and expects us to pay her back— that she deserves a right to make profit off of the song. How is that possible if she did not contribute to the actual writing or production processes of the song? Is there legally anything we can do? The writing and production credits have not been legally registered yet (I have witnesses who experienced the writing process firsthand, I’m not sure if that helps). Since nothing is formally on paper, would that give me any sort of advantage?

          Also: she recently stated that the other artist decided to allow her 25% of his 50%, and then argued that since she paid half she deserved half of all profit, and then changed her argument again. I don’t know where I stand in this situation at all, especially as a minor (I don’t turn 18 until June).

Update! Since we told her she has no claim to the lyrics of the song, this lady is threatening to use the background of the song and give the song to someone else, with different lyrics! Is that even allowed?