I would go back to underwear. And she will likely have a number of 'accidents' before she is trained. Do not make her feel bad when she has an accident. Just keep calmly telling her pee and poop go in the toilet. Just remind her to go to the bathroom when she wakes up, after each meal, before bed and if you notice she hasn't gone in a while. If she is really having fun playing, she likely will not stop on her own to go to the bathroom unless you remind her. We did not do any kind of reward chart/stickers/anything else with DS (25 months at the time). More than 50% of the kids in this world are trained by 12 months (article in the NY Times a few years ago, lots of source material) so this late toilet training is a US specific thing. Also babies in this country used to be trained earlier so I wouldn't worry that she isn't ready. Now that disposables are so easy there is less parent motivation so kids are not trained. I think your motivation is absolutely reasonable. My mom had me trained at 12 months because my sister was due 1 month later and she was not going to have two in diapers :)
In the 1950, almost a 100% of children wore cloth diapers and 95% of these children were trained by the age of 18 months.
In the 1980s, about 50% of children wore cloth diapers, while the other 50% wore disposable diapers and only about 50% of the children were potty trained by the age of 18months.
Today, almost 90-95% of children wear disposable diapers and only about 10% of children are potty trained by the age of 18 months.
Today, the average age for potty training is about 30 months with the age ranging from 18-60 months (that's 5 years old).