If it's flat where you live, you probably have wind. I'd get a fully geared bike for a first bike. And if she is unused to riding much, or long distances, the more gears the better. I live at sea level, and use all 3 chain rings routinely.

If you want her to enjoy riding with you or other presumed roadies, she will never be happy with a fixie, nor able to keep up.

What kind of bikes has she tried out so far? SHE MUST test ride them before you buy. And she should try a variety, from fixies to a couple high end carbon or aluminum road bikes just so she can appreciate the differences from one to the other and see what technology is available at different price points. Using the extremes will help her to narrow the type of bike she wants, then you can start looking in your price range.

Honestly the Trek FX series is a really good choice, and lots of TE members ride them for errands tricked out with panniers, or just as long distance road rides. I almost bought one myself a couple years ago but chose instead a bike with dropped bars.

Later, if she wants another bike (and she probably will if you did well with the 1st one) then look for the other stuff - fixie, single speed, folders, or touring.

Good luck