Today Joe said "Isn't it weird that Dee Dee's name used to be Destiny?" and as soon as Dee heard that last word, her ears perked up and she turned to look right at us. For the next 10 minutes, we called random words toward her, but she only turned when she heard Destiny. It's funny/sad that we thought we could just stop calling her what she was called for 7 years, but I'm glad we figured it out. She's still Dee Dee to me, but we'll call her the correct name when she's in earshot.
For the record: Lucky has only ever been called Lucky, but he is too dumb to respond to it.