You don't mention what size she is but...is this similar to what you're looking for? I find a lot of patterns on eBay. Hope this helps:

Here is a link that might be useful: ruffled skirt

if the waist fits, why not just add another
ruffle to it. let her pick out the material and
she will love it. should only take 1/4 yd.

gerryo

Another vote for just adding another ruffle. Measure the last ruffle on the skirt, double that amount and cut a strip of fabric how many inches longer you need and gather it up. Sew onto that last ruffle, hem it and you have a skirt that will fit a few more months.

I agree with Gerry and Jenni about adding another ruffle...if it's a "tiered" skirt...
My understanding of..."It's a little cotton job with a band waist and three lines of ruffles sewn onto the main body of the skirt."...is that it's a straight or A-line skirt with ruffles sewn onto it. If that is the case, another ruffle may not help if your daughter is growing out of the skirt, and not just getting taller. It may be time for a larger pattern. Did I understand right about the type of skirt?
I'm having a similar problem keeping up with my growing GDs' sizes, and have found quite a few patterns at reduced prices on eBay. Good luck with your skirt.