So what does your wife actually want to do? It looks like she has expertise in areas that rely on "soft" skills. Unfortunately, because these are difficult to quantify or measure, they tend to be undervalued by employers, who tend to think that they can just get another "people person" to fill the role. For the same reason, this can make it hard to find a better job, because it is hard to distinguish yourself from all of the others out there.
So my first question is does she want to stay in her current field? If so, are there specific skills, areas of expertise, certificates, or other "things you can put on a resume" that she can develop? If she generally likes the work/field, I would focus less on the immediate pay and more on using her current employer to develop quantifiable skills that improve her marketability. Then, in a year or two, she will have a solid base of support to justify the raise she wants -- and a much better resume if they don't fork it over.
OTOH, if she doesn't like her current field, then she can quit and try to build her own design business or follow whatever other ideas she may have.