I just started trying to learn on my own (guitar). My fingers are slender and pretty long for a woman and I still can't play the f chord. I always seem to have a limitation on an instrument. If that's your passion (the guitar) keep on. I think that you should get a second opinion by another teacher. A teacher once told me that a student in high school played the clarinet but he thought that she would do better on a flute and he was right. Get at least two more opinions from good teachers or players.