Rhyne's defensive stats the last 5 games haven't been so bad: 10 steals, 10 blocks, 38 rebounds are all fantastic numbers for a guard. She does have a reputation for taking defensive plays off, but if she committed to it all in (like she'll need to in the WNBA) I think she'll be a very good 2-way player. She has the tools.
Stats don't tell the full story, of course. I don't think Tamari will win the award, but I still can't think of another current player that strikes fear in the hearts of opposing teams trying to shoot over/around her than Tamari does...and that includes Aliyah (who I presume will be the winner).