We have already been told "Renee from Bridget Jones's Diary" ? Not fashionably thin does not automatically mean actual plus sized (plus sized models are generally on the smaller than average size which really does mess things up!)
So for sci-fi fantasy:
I agree with the suggestion for Dawn. She is perfect for any woman so long as she picks an iteration she is comfortable with. I love her Battle outfit for instance as it accentuates the curves but doesn't leave you feeling exposed.
It plays up strength and femininity, and can be sexy too depending on how you portray her.
Bariss is great and Shaak Ti was a tall model but her costume does allow for being able to hide in folds of fabric. It's why I'm making a movie version to go along with my Force Unleashed (this latter is a great costume for a woman who is on the more muscular side of the wide spectrum of female forms- full body paint also works great for illusion but is can be terrifying to contemplate!)
Poison Ivy would be brilliant, especially if built on a good foundation.
Historical:
Saxon court gowns a la Cranach. The prettiest prettiest [rincess type dresses ever. Truly. They look amazing on curvy bodies, so a ful bust with little waist is ideal.
Now set aside the aesthetic styling and look at the shapes:
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File:1516 Emilia.jpg - Wikimedia Commons
File:Cranach the Elder Girl with forget-me-nots.jpg - Wikimedia Commons
File:Judith mit dem Haupt des Holofernes.jpg - Wikimedia Commons
File:Lucas Cranach d. Ä. 026.jpg - Wikimedia Commons
Natural form and both bustle eras are also ideal (any other era also but these really really flatter a curvier rather than leaner body type- at least to the modern eye
.)
Another would be Christina Hendrick's character in Mad Men. The hot pink dress would probably be most recognisable.
Otherwise as someone else said: anything she wants as she is most certainly not in the overweight category.
The right fabrics and fit also really help with confidence- my Catwoman and Mara Jade suits are made from MJ Trends PVC. They act a bit like full body corsets and give a good 2" butt lift. I feel very comfortable in them. Not so comfortable in softer stretchier lycra bodysuits as they don't give the same support.