Megie, DD2 who is 3.5 still has a dummy but ONLY at night. I found it easy to take it away during the day, and we are telling her from recently, that santa will be taking the dummy. It means she'll be 4, but as she only has it at night Im not fussed. Maybe your friend could start by removing it in the day. Definitely easier than at night. I started by not sending it to daycare and she was fine, then I told her its' ONLY for bed time!
xo