By limitations of the game, Dina has to be Caliente if Nina is. If you want a real-world type reason for it, then I think it's perfectly sensible that Dina would not want to be calling herself by the name of her last husband, considering he was apparently Bella's brother, which I'm sure would raise a few red flags for Mortimer.
And if the surname didn't raise red flags, Dina's age should
. Dina's memories are odd too. She reckons she had her first kiss with Michael as a teen, which is not possible unless teen Dina had her first kiss with Adult/Elder Michael.