You don't mention if it's just a facelift you want or if the UX/flow needs help too. Speaking from experience, it is often painful for everyone to have these r

You don't mention if it's just a facelift you want or if the UX/flow needs help too. Speaking from experience, it is often painful for everyone to have these roles come in after-the-fact unless the design is really barebones or built with something like Foundation or Bootstrap. Are you willing to completely scrap what you have now from a design perspective if they feel strongly that it needs it? Do you have engineers available to help fill in the programmatic gaps the designer can't code out themselves? I'd also echo others here and say this is not the job of an intern. The icons, maybe, but if you're looking for someone to really help you out with web app design, you would be better served by someone with actual experience working on other products lest you want to end up with something you'll just need to pay someone more to fix later. As I insinuated in the last paragraph, try to find a designer that can code so you can bypass any potential problems with Photoshop comps not being built out correctly, especially if your engineers are not design-savvy, aren't comfortable with CSS or have a tendency to use mockups more as suggestive guides than an official proof.