Well, nicknames are fun... especially for a couple. I always liked calling my girlfriend, babe, or babie, sweetheart, most of those are pretty coming. Or, you could try *** (like a cat) (not a good choice to use around her parents), or pus pus, or maybe *** pus. If she's not a fan of any of these you need to be the creative boyfriend that you are and give her one.
If she doesn't like any of the names you have for her, maybe that's a good indication of what kinda of match you make. There are plenty of girlfriends who would love to be called *** by there boyfriends!