Sorry without you seeing the tests she has been given, her responses, and the scores this is possibly all pretty meaningless. Dyslexia screening tests are pretty crude and cheap and cheerful.
There are so many different dyslexia definitions it's all a bit of a strange area. The important thing is to find out what your daughter needs to be taught so that her spelling is as good as you would like it to be, and that her reading faults ( whatever they are in addition to missing out words) are ironed out.
A lot of schools are not great at teaching the early stages of reading, and not great at teaching spelling in any systematic way. This is the result for many children - inaccurate reading and poor spelling. The school is probably saying she is "dyslexic" because her spelling and reading accuracy do not match up to other aspects of her ability. Of course this could be for numerous reasons.
Look up the BPS working definition of dyslexia and you will see that it is the teaching that is key, not a one-off assessment to diagnose whether or not a child has "dyslexia".
Try looking at http://www.dyslexics.org.uk
and stop trusting any "dyslexia" expert that you meet unless there is good reason for trusting what they say. A lot of it is old fashioned out of date nonsense and what is needed is for the child to be taught the right things.
Of course there's a good reason for a "dyslexia diagnosis" if you want your child to receive extra time in 11plus and SATS etc, but the last thing you really want is for a ten year old to be given a laptop and spellchecker and someone to read when all she needs is to be taught to read accurately and spell better than she does currently. It's not rocket science but some schools make a load of hocus pocus out of it.
I can see it is likely happen to one of my children at the moment; the school has given them all a half-baked spelling test at the start of year 2, she has dropped spelling groups as a consequence and is back to receiving reception type spellings. They don't teach spelling well in school and the stuff that is sent home is rubbish so unless I do something, or she is just a "natural-born speller" (which she seemed to be until school go their hands on her!) there's not much hope of her becoming a good speller.
Some schools are extremely annoying. My year 2 daughter started holding a pencil very badly two years ago in reception. I've mentioned this to them loads of times, they have done absolutely nothing, not even shown her how to hold it correctly. Now in year 2 the head says it might be too late to do anything! I'm sure that at some point they'd love to do a "dysgraphia assessment" to show that there is something "wrong" with my child.
This is probably nothing at all to do with your daughter, just the way she has / has not been taught.
When you think about it logically, what's the big deal about her missing out little words? She has just got a sloppy reading habit. She needs daily nitpicking exercises to make sure that she always reads from left to right and doesn't miss out words. She's is perfectly capable of that I am absolutely sure. And who know if she is missing out words when she is reading in her head or if she just is being sloppy when reading out loud.
There's so much hocus pocus and bad science in this area it is maddening.
Your daughter needs teaching the right things, that is all. Try communicating with an EP like Derrie Clarke on the RRF website to get a better grasp of all this.