As others have said, the formal certificates aren't necessarily an indication of the quality of the instruction. The most important question is, are you achieving what you want to? If you are learning to dance what you want, feel you are progressing pretty consistently, and are able to use what you learn in the venues where you want to dance, then I'd say your instructor is pretty good--for you (that's not to say she'd necessarily be good for someone whose goals are different).
If you want something more "objective" to compare her to, here are a few ideas:
1) if there are other studios in your area, take a group class or even a private lesson there, just to see what else is available and how your instructor compares
2) if you know any of her students who have been taking lessons from her longer than you have, how does their dancing look? Is that where you want to be in the future?
3) the most strigent comparison would be to go to a competition (try accessdance.com to find out if there are any in your area) and see the newcomer and bronze level competitions. How does your dancing compare to those competitors? Competitive dancers will likely be doing fewer "moves" at a given level than a purely social dancer, but will be (aspiring to) doing them with the best possible technique. Still, you'll get a broad idea of what a lot of other dancers at more or less your level can do.