I agree with learnandsay 
dd2 has a best friend who (youngest with very bright older siblings and driven, though very nice, parents) constantly competes, and always needs to be better/bigger/faster.
I think giving a little, simple but not judgemental, understanding about people who do that can be helpful - its certainly helped dd2, who gets annoyed rather than upset most of the time now, and has learned to ignore the bulk of it.
I have simply talked to dd2 about how some children worry about not being enough, and think they have to be 'better' - though of course they are fine as they are, just like she is. In her friend's case, I've explained that poor old X has two big sisters, and probably finds it very hard to relax as she's fed up with being the littlest.
I've also given information about how all children have their own, special way of learning to read etc - and that they all end up in the same place, but take different journeys to get there, and that she has her own special adventure to reading. For some reason, that one really appeals to dd2 
If your little dd does turn out to have dyslexia, understanding about it, and knowing its a) not her fault and b) doesn't make her less than anyone else - its just a thing that happens, like needing glasses, or not hearing properly - might help?
Showing her that you think her reading is great, and that its not a competition to you, is important too - but I'm sure you're doing that already!
Horrid seeing our children stressed, but they do grow so much resilience through all of that stuff - with our help. Easy to say, as I have an older one and have seen it, but its true 