It's really hard when you have a difficult child. ImOverHere, you have my total sympathies.
DS (aged 4 and 2 months) has been really objectionable since he was 2. DH and I were in pits of despair with his constant rages, poor sleep patterns and generally difficult behaviour. We were walking on eggshells around him and I actually was afraid of him for a long time because of wanting to avoid his easily triggered fury.
I can categorically say I did not like DS during this period. He got lots of hugs, positive words, came into our bed at night whenever he wanted etc but I did not like him, I'd say for 80% of the time.
And whilst that is far from ideal, we're all human. If you have someone who is constantly difficult and challenging in your life, it's natural to have negative feelings about them.
The difference is whether you show those negative feelings. Obviously, if your DD is being annoying, you can think all the things in your head that you would like to say as a release for some of the pressure you're under. But don't say them. You can still show her that her behaviour is unacceptable by being firm and calm in your rejection of the behaviour.
Don't take what she says too seriously. Lots of 'no's' etc - she might not really mean what she says. I just ignored my DS's no's and other unhelpful spiel. I pretended he didn't have a clue what he was saying and that helped.
Erm, in fact, my mantra in difficult times was, "This too shall pass, this too shall pass," and "Don't be too hard on him - he has special needs," or I would pretend he was someone else's child in order to get some detachment from him.
Also, walk away from her if she is being problematic. If it's to do with getting dressed and stuff like that, put her in the car in her pyjamas and take her clothes and shoes with you so that when you get to where you need to go, you can put her in them. Or not. It doesn't matter.
The good news is that it gets better. I kept DS busy with activities that burned his energy like football, mini gym and swimming and lots of playdates. I know that my friends too found him difficult and I really thank them for putting up with him on these playdates!
Bear up. It does get better over time. Try to anticipate when she gets difficult and think of ways to circumnavigate those flash points. Or write them down on MN and we could come up with suggestions?
Sorry for ramble. I just feel your pain!