My black lab was Madame (Mademoiselle), Dalmation was Dottie, Blue Great Dane was Pumpkin, Boxer was Cindy and Boston Terrier was Daisy. Our friends St.Bernard is names Maggie. Congrats and your new dog. I bet she is beautiful!!!
We name after deceased rock stars, so we have had a Garcia, we now have Hendrix and Marley. For a female our next choice is Joplin. For a St Bernard maybe "Mama Cass" ?
I always liked D.O.G. You might as well name her Bitch (you're going to say it a few times anyway). If you had two of them there is always, Come and Stay.
Our's is name Sophie. Gretchen would be a good name for a St. Bernard. I've hear that two syllable names are best for training a dog.