I have a 7 year old daughter, myself, and its commendable that you are taking such a huge interest in her well being and education. My wife and i, always stay on top of her work, homework, preparing for tests, and current curriculum. On face value, it does, maybe?, seem like you may be doing a bit much, since she is only 6 and in first grade. However, if your daughter is enjoying the extra work, and is not showing any signs of it being too much, or buning out, then it should be fine. At 6 years old, and in first grade, the work is still basic, but it is the foundation for the next few years to come.
You want to make sure, she knows her alphabet, and numbers. She should be aware of certain "memory" words, that make her able to read on a first grade level. Words like, THE, AND, CAT, RUN, and such. Certain repetition is the key. The basics of math, like plus and minus. Really just simple things like this, for her age group. We sometimes expect them to understand more, or be able to grasp full sentences, and problems, but we must make sure that we are not expecting too much of them, at this age, either.
I would, definately, talk to her teacher, and pick the teachers brain. See what the teacher says about her progress, abilities, and in comparison with her fellow students, where she is. You may find that she may be doing perfectly fine with where she is supposed to be in her work. Every child learns at different levels, and paces. Try not to compare them to other siblings, at that age, or even ourselves, at that age. Really, keeping an open relationship with her teacher, is key. See what the teacher says, thats the first and best place to start. Also, keep her teacher on the same page, of what you are doing. Tell the teacher all about the extra tutoring, and sessions, and the specific work you are doing. See what the teacher thinks about it, and or recommends too.
Hope this helps, and remember, at 6 years old, we can only expect so much from them. All things will become clearer, and work out in time.