a trainer with a broad background, which maybe includes pilates, would definitely be better than someone with a more narrow focus (regardless of the content of that focus.) it's a truism that many pilates instructor-types have dance backgrounds and/or are used to working with dancers.... so that would be a good thing for you.
but i agree in general with the advice in this thread that you need resistance training, whether with a qualified trainer and/or a physical therapist. that's what gets you strength. i would avoid group classes like the plague - they are bastions of bad/harmful technique and non-useful peer pressure, plus don't feature sufficient personal attention. unless the activity is something with a low injury potential, i'd avoid.
i have a pilates instructor who is in school studying to be a physical therapist (also has a traditional personal trainer background) and i have to say, i find the combination hard to beat. because she's seriously interested in rehabilitative/preventative therapy, she's ideal as an exercise trainer. her goal is NEVER to force me into an exercise when she sees it doesn't serve me... for example, mat pilates uses lots of "chin tucked to your chest" ab exercises that kill my sensitive neck. in a group class, i will usually at least try to do this move along with everybody else - usually to my own detriment. a pilates dogmatist might insist i continue to try, wheras this teacher, wisely, forbids me to do it until we figure out together how to reduce my neck strain safely.