It sounds like she does struggle with some math concepts, but I don't know if I'd go so far as to say it's a math disability.
My son has never been officially diagnosed with a math disability, although we all (teachers, me, his dad, himself, etc) recognize that there's a disconnect somewhere. He's 16, in 10th grade. He does not know his times tables. He memorizes some of them sometimes and even remembers them for an afternoon. But the next day it's like he's never seen it before. For him, 3 x 7 = 21 is a totally different equation to 7 x 3 = 21. And 4 + 5 = 9 has absolutely no relationship to 9 - 5 = 4. They are 2 completely different equations. And seeing the relationship between the multiplication and division just doesn't exist.
He can count by 10s, but if you ask him what's 4 x 10, he'll use his fingers and count it up all the way to 40. You should see him do 9 x 9! Takes him a while to get that. And he has to do it EVERY SINGLE TIME. He has memorized the steps to do long division, and he sometimes even gets the answer correct. But it takes him a really, REALLY long time to get through one problem.
He cannot tell time. If he has to meet a friend at 3 and it takes 15 minutes to get there, he wouldn't know what time to leave without us telling him.
He's been in special math classes since 6th grade. Once, in 7th grade, he brought home the exact same math worksheet for homework as his sister in 4th grade. She wizzed through it. It took him an hour. With our help on every problem.
He's in Algebra now because our state requires Sophomores to take a statewide Algebra exam at the end of the year. He does not belong in Algebra. He will fail this exam. I'm not saying that like I'm judging him. I'm saying that based on all of our math experiences. Luckily, his year is the "guinea pig" year with this new test, so he won't have to pass it to graduate (the kids a year below him WILL have to pass to graduate). We dodged a bullet there.
So to answer your question, your 6yr old is having difficulty in math, but it seems pretty normal for this age. My now 11yr old also had some difficulties with math at that age. She is also the youngest in her class. Now, in 6th grade, she has a solid 98% in math, with barely any effort. It just clicked for her. Your little girl is being introduced to concepts she's never seen before. Chances are things will click after a while. Some of the things she's having difficulty with might just take some practice. She can do addition and subtraction, so she's getting some of the building blocks she needs. I'm sorry to hear she's starting to hate math. I like some of the suggestions to try to make math fun, or sneak in some math when she doesn't even realize she's doing it. If the difficulties continue, a tutor might be the way to go.