First off, you are doing a great job!!! Keep that up.
I've listed some questions to ask yourself. Sometimes that helps unlock the key.
* How old is she compared to her peers? Is she younger?
* Any complications with hearing or sight as a baby? Did she talk late?
* Get her eyes tested.
* Does she know her numbers and recognize them? If so, then it may be specific to you explaining that the letters are just funny little symbols (or pictures) that represent the sounds that we make when we speak and sound out words.
* Take it down to 2-3 letters a week and then add 1-2 every few days as she masters them. Make an incentive chart with the letters on the top (lowercase too) and put a sticker under each one she masters. Give her a small toy or piece of candy (whatever works for you) for every 3 letters she can do. The more you give, the sooner it will happen. (Do this when you need to teach sight words, math facts, etc.)
*Constantly quiz her about letters you are working on or have mastered. "Can you find an 'e'?" When you pass Target. Esc. Or ask, "what letters do you see and where?" Give her extra points towards your incentive chart for those. Promise something bigger once she knows them all. I wouldn't put a name on it in case she really can't do it yet and you want to get that item for Christmas or birthday. Just say "something big like an X or an X."
* Make it fun. Use shaving foam on a plate and write the letters for her to tell you. Get out alphabet cereal and let her eat all the 'e's. Same with alphabet soup.
*Give her a reward (sticker) if she can name the letters out of order than the way you've practiced.
* Really watch to see how she learns best. I had one kiddo I tutored that only learned material if she had something to physically do with it (esp. abstract concepts - like letter recognition....'A' means nothing). So, I gave her cards to manipulate. Have your daughter match up 'A' with 'a' and with a picture of an alligator. 3 cards. Start with upper and lower and then add the picture. Does she learn best from technology? Plenty of games out there. Watching tv? Super Why and Word World are great shows for that.
If you can't work with her, then yes get a tutor. I've tutored for kids that have parents that are teachers. It was such a reality check for me. :) Kids just don't want their parents to have that role.
If she cannot start picking them doing all of this, then I would talk to her teacher about being assessed. (It is free for you when the school does it.) I would especially do this if math is much stronger for her. Typical kids with a learning disability (I hate that phrase....everyone learns differently) have a strength in one area and struggle with another (great math, lousy reading)
I'm guessing she is feeling overwhelmed with so much to learn and KNOWS that the other kids are getting it. She may just be shutting down. Talk to her about it and pep her up. Tell her that no matter what, you will help her learn all of this crazy stuff.
Best wishes, mama!