Is she 100% fluent in Spanish?

She is DEFINITELY not 100% fluent, even if she grew up with some relatives who were. Plus, her mom definitely appears to be a dominant English speaker, at least from the few interviews I've seen with her, so it seems like Eva is at least third-generation. Listen to any interview she's done in Spanish and it's apparent in the first 30 seconds that she's not all that fluent. What she is able to say is rather slow-coming, intonation is a little off, doesn't speak with much complexity, etc. But yes, she can speak in complete sentences in a "controlled" context. I don't think she'd do that well just going off the cuff.

You explained it so well I'm not going to say anything else. If any of you do understand Spanish here are examples of her trying https://www.youtube.com/watch?v=HD-jayvKYa4 and https://www.youtube.com/watch?v=UI56r0K8EDE and it's exactly like you said. I think she has gotten better through the years. I believe her boyfriend is the president of Mexican conglomerate Televisa. The U.S. Latino that speaks the best Spanish in my opinion is Marc Anthony.