Obviously the name you choose has to have some significance attached to it. Choosing her Maden name seems best but this may depend on the significance you both attach to it.
You could try researching family history a little, perhaps there's a significant female ancestor that you could both feel an affinity with that you both may seem as paying respect to.
You could also consider a word or name that is significant only to yourselves for example her first name and/or surname/maiden name turned into an anagram which become your name, this way it is unique and significant.
The problem with choosing a name that you simply have something in common with but no real afinity with is that it may seem a little "Mickey Mouse" and you obviously want the name to make a statement about your D/s relationship.
Sorry, I don't think I've been much help.