HI L.,
Yes take her to a pediatric opthamologist right away. We had no idea that our daughter had a lazy eye until her 4 year check up. They covered her right eye and she was immediately ducking out to try to see. Turns out that she had almost no vision in her left eye. The sooner your daughter gets treated for this the better chance they have to improve her vision.
Just a few other tips... if they do diagnose her with a lazy eye and recommend a patch, I would advise getting a "framehuggers" patch. We went through 2 patches and a lot of frustration before we ordered one of these. They fit right over the lens, so you don't have to worry about the patch slipping around or then seeing from the edges. We now are able to use ointment that dilates the healthy eye and that has been terrific. It is more effective and needs to be used less often than the patch, but I think the weak eye has to be to a certain prescription before they will let you use the ointment.
Also, if your daughter has to wear glasses and you can afford it at all, get her a second pair. I didn't realize how easy it was to get glasses made and we waited weeks to get her fixed after she'd break them or lose a screw, etc... Kids are hard on glasses and I can't believe it took us so long to get a second pair. All you need is the prescription for her lenses and you can take it anywhere that they make glasses. We went to Lenscrafters, which is expensive, but was worth it to me.
Good luck. Feel free to e-mail me if I can help answer any questions for you. Our daughter has been wearing glasses for almost 2 years now.