Generally, a dyslexic person will not get all the words right one day, and not the next. If the words are complex and haven't been previously memorised, then she won't be able to get them all right, if she is dyslexic.
There are different reasons for a child to have difficulty reading. If the child's brain is still trying to sort out which side is dominant, sometimes this can cause confusion with mirror imaging. Letters like "b" and "d" will be difficult to distinguish. Or letters will be out of order.
Other problems can be due to the eye not tracking properly form left to right - again, this is something that has to be learned as we learn to read, but if for whatever reason the link between the brain and the eye movements is still immature, then the child's eyes will be flicking all over the page instead of in the left to right along the line sequence. This will mean the WORDS reaching the brain will be as if they have been randomly selected on the page, and of course won't make sense.
There are things you can do. Testing should also be possible - the professor where I used to work would wire me up to an oscilloscope to demonstrate these eye movements to the medical students. There's no faster way to learn this stuff, than to be "exhibit A"! Wiring up is easy (if you have the equipment). A neuropsychologist could do it, should have all the equipment. It's something that could be done alongside a simple EEG. They just need to track the movement of the eye muscles (electrodes to pick up the signals). A good track looks like a staircase on the oscilloscope screen. To confirm this, filming where the eyes are looking would confirm if the child's eyes are correctly tracking.
A simple exercise to train your child's eyes to track correctly - won't do any harm if things are already working well. You find a ball and get the child to roll the ball from left hand to right hand, while the child also stares at the ball. The child catches the ball in the right hand then passes it back to the left UNDER the table. Then he should roll it again. If you use a ball that is fun, brightly coloured or in some other way attention-getting, this is even more effective. The exercise should be repeated with about five to ten rolls then have another short session later in the day. The more sessions the better.
This is cheap - the cost of the ball is all. I bought some balls that are tricky - they are double. There is a coloured ball that looks like an eyeball, floating on fluid inside an outer clear ball. The outer ball is the one that rolls; the inner ball is weighted so the "eye" is always staring up, as the whole complex rolls. It looks like it's sliding across the desk, kids love it which makes this a fun exercise.
Remember - that exercise is to train the eye and the brain to get into the pattern of tracking left to right, which we need in order to read a line of print well. It can also help establish the brain dominance problems, but this IS just one thing to do - if you believe your child could be dyslexic, she does need to be professionally assessed. All I have suggested is the sort of exercise you can do for her at home, on top of professional help.
With any learning problem or disability, the person learns to adapt. Sometimes there are limits to how well you adapt, but people each find their own way. Professional help can speed up this process. So can careful parental observation coupled with lateral thinking and support.
A tip to help with the letter recognition and reversal problems - my dyslexic nephew was taught with a very visual system. I also remember when I was learning to read and felt I needed an assist to get it right more easily.
Think of the word "bed" in lower case (as here). Look at it - the letters themselves make the picture of a bed, seen from the side. The two uprights are the bedposts. They are each on the outer end of the word. We remember how the word sounds, so we know that the first letter is a B (because of the sound it makes). Similarly, the last letter has to be a D. The round parts of each letter plus the E in the middle make up the mattress (or maybe a pillow at each end also?). That was mine, anyway. I was trying to think of other aides but by that time I was finding I didn't really need them.
My nephew learned a range of these - he was taught that he had to begin writing the letter from the left and the top. A letter with a round bit, you tend to begin with where it attaches to a stalk. So writing the lower case "g" you begin with the edge of the round bit at the stalk, move the pen down and around clockwise then back to the top and down, for the stem. By always moving the hand in the same way, this is also helping to program the brain to always go in the same direction. And to help him remember to do all this and that this is "g" and the sound it makes, he was told to thing of it as a girl. The round bit is the girl (or her head) and then the long stem with the curl at the bottom is her hair that she is sitting on.
For each letter there can be a story to help remember.
I don't know all of them. My sister was taught about this in a clinic in Sydney, decades ago, so she could continue working with him after they went back home to their place in the country. She might remember the list if I asked her, but it should be widely available if there's any merit to it.
There is always a way. Being inventive and imaginative can help a great deal.
Marg
mom! You will figure out what the school recommends and then speak to her doctor about additional testing. This can be helped. 
