My wife currently has a road bike. But she simply can not find a position which is comfortable for her. Her saddle has been moved forward as much as possible. She has a special stem which which is almost vertical. And she has brake levers in the top. But it still is not comfortable enough.
So I’m looking for a gravel bike frame which has a very relaxed geometry. And to put 40c tires with 700c rims if possible. Or maybe even bigger tires with 650b. She’s 170 cm tall and long legs. So the reach should be quite short.
You might need to give a bit more context - what type of riding does she want to do? What speed, and what terrain? Does she want to train, or do you just want to be able to go for a leisurely ride together?
A hybrid/city bike might be better, or a light MTB.
She might have issues with the saddle. From the position you describe, it sounds like she can’t rotate her hips forward properly. To be honest, I think your best start would be a bike fit preferably with a female fitter! I don’t think just a different frame will do (unless her current one is very obviously too big).
Has she had a fit done by someone who does fits for a living? It really does sound like she is either A.) On the wrong size bike, or B.) Having unrealistic expectations of comfort. I would start with the fitter. A good one will put her on a fake bicycle that they can tinker with the fit until they get her in a comfortable and ergonomic position and then give you all the geometry numbers so you can search for frames with those numbers.
The way I read the original post was that you were not systematically changing her fit, but just trying to get her more comfortable on the bike by making individual changes. As part of a bike fit, your wife should try several saddles, handlebars, etc. The bike fitter should also make sure that the bike is in the right size. Just going by body height usually works, but can fail spectacularly if e. g. your wife has unusually long or short limbs.
The other thing I’d recommend is that your wife test rides several bikes and several kinds of drop bar bikes. I had an endurance road bike and I did not like the geometry, for example, even though it was fitted to me. The fit was alright, I could never get as aggressive as I wanted to be.
Also, you did not mention how experienced your wife is and what her expectations are. Many beginners, for example, equate softer saddles with more comfortable saddles, but that’s of course not true: many soft saddles are more uncomfortable for longer distances since a larger area of your S.O.’s bum may go numb.
Lastly, if speed is not of the essence, IMHO she should also try flatbars. I still find flatbars more comfortable, and if I didn’t want to go super fast on the road, I might actually go down that route. Quite a few companies make “road bikes with flat bars” under various names. There are also MTB-derived bikes that fill the same niche, but from the other end. My mom and my sister have such bikes, and they love theirs for their purposes.
In all honesty, I’d recommend withholding your own ideas for a bit. If cycling is something she’s interested in, let her have a poke around a bike shop, have a few test rides, and see what she gravitates toward- if she doesn’t actively engage in the process of finding a bike she’s actually excited to ride on her own terms it’s very unlikely that she’ll do so, and you’ll be down more than a spare groupset.
You don’t need anything fancy or specific to get into cycling, just enjoyment. The latter is a non-negotiable.
(For what it’s worth, My partner rides around on a neon green banana bike with a basket on the front for beer, and I think that man has more fun than my entire group ride combined.)