Nobody to get Arts supplement rec letter from??

<p>So I'm submitting an arts supplement to Stanford (for violin) and for this they require a recommendation letter from a music teacher or mentor. The problem is, MY DAD is my violin teacher. Obviously parents can't write recommendation letters, but my dad is the only person who has ever really taught me. My orchestra teacher at school knows me well, but I've been late to rehearsal so many times and probably frustrated her so much with it that I wouldn't trust her writing me a recommendation letter... So I ended up asking a German cello professor who I've performed with before to write me one, and when she showed it to me it was really positive but it was also extremely generic and contained countless grammar mistakes, which makes me not sure if it would be good enough for Stanford. But right now it seems like my only option.
What else can I do? I really want to have a great recommendation so that I can go to Stanford. Any advice would be appreciated! Thanks!</p>