Hi welcome to the forum. If your gf tested positive on the IgM then she most definitely has Lyme and should've started treatment immediately. The longer she waits the tougher it will be to "cure".
I'm guessing she saw her primary doc or an infectious disease doc because a Lyme Literate doctor would have started her on abx right away. Very important she treats with an LLMD or a naturopath specializing in Lyme and not an infectious disease doc or PCP. Good luck to her!