To echo others, no she cannot put a curse on you. She sounds like she's working from fear and intimidation. You can answer next time she calls and tell her you view it that way (which may shock her into leaving you alone), or just not bother responding. Also of course you could try the BBB option Erin mentioned.
I don't think it's ethical to work as a psychic from a power-over intention. You're the one who has power over the shape and course of your life - not her. Even with her "mediocre" abilities. Psychics who are secure in their gifts and who make an ethical, positive contribution aren't likely to approach things in such a scammy, fear-based way.