Can they garnish my check for a balance for my attorney if my payment isn't as big as they want?

I have an outstanding balance of $3800. I paid my retainer up front of $3500. I asked at the time if I could make payments once my retainer was used up because I wouldn't be able to pay more than a payment after that. My attorney told me I was able to make payments and would be charge 7% interest. I have made payments over the past year every month including her retainer fee of $3500. I have made payments consisting of at least $100 and some months more than $100, when I am able to pay more. She just sent me a letter telling me she wants me to pay $500 a month. I cannot afford $500.00 a month. Can my attorney garnish my wages for that amount or more? Any advice or information is appreciated. Thank you.