When I started to read this post I was expecting to see that you were looking for a western saddle. In that case, I would have said as long as the skirts didn't interfere with her movement or irritate her by bumping her hip every time she took a step. you'd be ok. Since you're looking at dressage saddles, then my answer is especially NO. They are so light and so minimally restricting that unless you find one that is really strangely built, she probably barely knows it's there, as long as it fits her withers, shoulders, back. Find one that's a comfortable fit for both of you. Riding in a saddle that's too small will set you back in your progress because you'll be so uncomfortable you won't be able to think of anything else.