It helps to know that a lot of kids are the same at this age. What are you teaching her that's so frustrating, actually? That might point to why the two of you are getting so frustrated. I used to be a kindergarten teacher, maybe I can help.
Try out fun ways of learning that don't involve sitting in one place, and going over what she's picked up at school.
If it's word recognition, take a few cards and write a word on each card. Pick common words that have a single beginning sound like door, window, ball, bed etc. Don't use words like "cat" which they can confuse with the "k" sound. Stick these cards at the appropriate places around the house - the "door" card on the door, the "window" card on the window, and so on. Leave them for a week, and keep pointing out the cards and identifying the words through the week.
At the end of the week, remove the cards, and write down the words on a sheet of paper. Asker her to match the cards with the names in the list. The trick with kids of kindergarten age is to mix learning with playing. Learning shouldn't seem like a chore, and it certainly shouldn't seem frustrating.
If it's number recognition that's frustrating, use the same card trick - place a number of these on the floor with a single number on each card. Play a game of Twister with a twist - ask her to keep her hand on the "7" card, foot on the "4" card and so on.
You could also try the bucket game. Line up 10 food buckets, and number them from 1 to 10. Collect 55 items from around the house - regular stuff, pencils, spoons, plastic bowls, her toys, whatever. if you can find 55 pieces of the same thing, like spoons, even better. Ask her to place the required numbers of items in each bucket. By the time she gets to 10, there should be no items left. Add one more bucket for "zero" - this is a nice time to teach her that the value of zero is "none" so she can't put anything in that bucket.
I hope this helped. If you need more such learning games, let me know. I'd be glad to help.
And please, don't feel like the "worst parent." We've all been there LOL. Just keep in mind, learning HAS TO BE FUN! And at this age, they can find fun in the simplest of things, which makes it easier.