Yeah, there should be some places. A group of us did this once for a friend's 40th birthday lunch. I forget the name of the company we used, but they wanted us all to submit info about the person. We did so, kept it honest and let the singer use a few liberties, but not so many liberties as for the party girl to be too embarassed.
Anyhow, they put together our submissions into lyrics and then the lyrics were sung for the party girl. If for your sister, you could do what we did. We hired the Kissing Bandit

))) He dressed up sort of like Zoro, all in black, with a mask and cape. He came in, was directed to our table, he came in with birthday balloons and flowers too of course.
and then on bended knee, with a rose extended, he sang his song and asked his beloved to come with him, his chopper was waiting on Macleod trail

))
It really was a lot of fun. anyhow, phone a few florists or those companies that deliver balloons, chocolates etc for special occasions. I think we found the company by phoning some of those balloon-o-gram places. If they dont do it, they can get you on to a company who does.