Ug. I really did have an issue with getting aggravated, and then get to deal with all the lovely mom-guilt of yelling or walking out. I did go to Love & Logic class and also got a couple of the books for my children's age, and it made a HUGE difference! My husband was skeptical, but he saw the change in me AND my son so much so that he sat me down with the workbook and we went over it together and discussed it, and he's started doing the same thing also. It helps to have that mindset of saying, "I know that you want to play with the book but it is not play TIME. It is bed TIME. If you want me to read the book, stop doing that and let me read. If you do it again, I will just kiss you goodnight and you can go to bed. It is your choice". Then if it becomes an issue, you just say "Aww, that is so sad. I know you want me to read, but you are not making the right choice". And leave without getting angry. HOWEVER, this is an all the time thing with us. It is SO much better than it's been before (for all of us). I know it may sound stupid, but having that script in mind ahead of time helps me not get frustrated or angry. Instead of having my emotions build up as I fight over something stupid, I just say "this is what is going to happen" and know that it will, and that helps me not get upset, which helps me teach and model the behavior I want my kids to pick up from me, and helps them understand that everything has a consequence, good or bad.
Sometimes I get mad and yell instead (usually when really tired myself)...I'm better but not perfect.
But one thing I am big on is apologizing. If (when) I mess up and yell out of frustration, I will calm myself and come back and say something like "Ok, when I yelled, I was feeling like __ because __. It is ok to feel that way. But it is not ok to yell (or whatever), and I am sorry." I believe it's important to show that parents have feelings too, and that feelings have reasons, but that even parents make mistakes and we need to say sorry too. If she's concerned with how she behaved, that is really good. Then you can say "I understand that you felt mad. But how do you think you should have handled it in this situation?" and it becomes a teaching opportunity. Of course you love her! You're showing her love by putting your arm around her, or holding her on your lap, and your tone of voice, now that we're talking about what to do next time. She'll know that. Once you've had the talk, I would say "Ok, now it is late, and time for bed. I love you, and I know you are a good and smart girl, and tomorrow you can make a better choice and have your story". (Some would read, I wouldn't).
We started doing this at 18 months for my oldest son. We had a problem with spitting. I started introducing the words "choose" and "choice" in normal conversation like saying "would you like orange juice or milk? your choice". Or "well, here are 3 movies to watch.....you choose which one you want". He knew those words because we used them everytime we could. Then when he would spit I would say "Spitting is not nice. If you choose to spit, you are choosing to sit in time out. If you choose NOT to spit, you are choosing to play in here with us". He didn't like time out (once a friend saw him spit on the time out spot, lol) but he did figure it out. We just do that all the time. At 4, dinner is now our big issue. If he chooses to cry or not eat, that is his choice. But choosing to not eat means he has to sit there and watch us eat dessert and then go to bed afterwards. Choosing to eat his dinner and being nice at the table is choosing to have dessert with us, and playing Superhero Memory and getting a story before bed. At 3 years old, he would tell his friends and my family "good choices make good things happen, bad choices make bad things happen". This is a good age to teach those things.
And congratulations on the potty success. :)