My 15 year old has 6 month by a 17 year old,who hasn't seen him since he was 2 months old,she found out he was on drugs and head he's in a rehab
Can she gave his parental rights revoked & the baby's last name changed to hers?

You are not going to get his rights taken away, unless it can be proved to the best interest of the child. If he has long term jail sentence maybe (and even then just maybe) She can get full custody, and fight any visitation the father wants, (does not sound like he wants any) and get a child support order, and ask judge to allow name change. (but even that may have to be shown to be in best interest of the child.) Is the father listed on the birth certificate? Is there any custody orders in place? Is there any support orders in place.

It may depend also on where you are at, some countries and if US, some states are easier and some places almost impossible.

Actually not visiting the child does not change much, if there is court ordered child support not paying that can be helpful.

How old was your daughter when she had the baby? Are there any custody or child support orders in place ?