Can't make a choice yet as I've only played through 2 of her 4 available options. Anyways, you might've given me a question that I cannot answer.
I think the best match seems to depend a lot on how I play her route and define her character through her actions. Say for example, if I choose to go with manipulative and 'hell may care'-choices with Diana's acts towards the aliens, then Graciela is a bit of a mismatch regardless if I like the character otherwise or not. And same goes for Alex's routes.
EDIT: PS. Will there be an "official feedback" thread for the game in general or should I just post where ever once I get that far?