I have a 4 year old that a nightmare to train. She didn't know how to make herself pee. She had gross motor delays, and I feel that carried over to the problem. We finally had a break through when she was just over 3. Then it took several months to poop train, and several more to night train.
My 25 month old can pee on the potty every time, and can stay dry most of the times in between....we just started last week.
My answer to your question is "when you kid can actually pee on the potty, have self control, and can communicate that he/she needs to go."
Training and practicing are the same in my mind. My daughter is a TINY thing. She can't pull her pants down by herself yet, or stay dry through naps. But, she is able to hold it longer and longer (training her muscles, and listening to her body) just in the last week. With her awareness of what is going on, I foresee night training and poop training very soon.
I think doing what you are doing, keeping it fun and not a chore will help. And, just keep fixes the problems you find. For instance, my daughter couldn't hoist herself on the potty by herself. We've gotten a stool tall enough, and UPS just delivered a new seat (a seat that has an attached little seat, and an adult seat) so that when she goes to climb on, it won't move underneath her and is shorter than the foam seat we currently have on there.
Don't give in on what you've started! It sounds like she has a terrific start!