ok, so would you let a 54 yr old drug addict see her grandkids?

i have custody of an 18 mth old girl, my niece, due to c.p.s. placement. her grandmother tested positive for meth, heroin, cocaine and marijuana 2 weeks before the final c.p.s. family visit to end the case and leave the children (there are 3 in all, i have the youngest, the 6 and 3 yr old live with the maternal grandfather) where they are.she has not gone to any drug treatment programs, parenting classes or counseling that was required for SUPERVISED visitation of the children. now she thinks she can pop up anytime to see the other 2 kids, but never calls me or has ever been in my house because she knows how i feel about her. today was an easter egg hunt she showed up to and when i told her to stay away from us she told me to ‘bite her as_’ and flipped me off in front of maybe 30 children and their parents. i will now NEVER let her see her again, am i wrong?
since so many people have responded i want to thank you all and add another detail to the story. for over 3 yrs this woman lived in the house with these children(not the baby, ive had here since she was 6 months old) and the only money she contributed was to buy more drugs when the parents were out. she has never taught them anything. the older children are grossly behind intellectually, the oldest is in his second yr of kindergarten, and the 3 yr old seems to be far behind as well. the baby, my little angel, is better behaved and nearly as verbally and socially mature as the both of them. kudos to me , and again, thank you for the support.