M.P.
You should take credit for her training. You did train her by talking with her and being a role model. I think that is a great way to teach. Congratulations? Of course she also "trained" herself by being ready to learn.
Do you have any idea why she doesn't want to use toilets? I'm wondering if it's because they're unfamiliar and perhaps you could "acquaint" her with others' toilets by just visiting them without using the toilet. Make it a fun thing to do. If she's fearful of the toilet's flushing sound make a game of flushing it together while you explain that she's too big to go down. Make it a humerous game. Sounds weird but it just might work.
She's only been using the toilet for 3 weeks. She might very well become more comfortable by the end of April.
Toddlers are frequently afraid that they'll fall in and get flushed down. The flushing sound of public toilets is much louder than that of home toilets. Does she have a small seat that fits on top of the regular toilet seat at home. Does she flush the toilet at home? I've heard of portible seats that fit over the adult seat. It folds up so that it'll fit in a diaper bag or tote.
Or perhaps she uses a little toilet chair.
If she has her own small toilet, take it with you to your brother's or have him buy one for her before you get there. When my cousin's son was a toddler he bought a second potty, just like the one they had at home, and mailed it to me ahead of time. We took it with us when we traveled by car and stayed overnight.
When my granddaughter was first out of diapers she also did not want to wear one when we were shopping. I found that sometimes we were too far from the rest room to get there in time. When were at the park there were no toilets. We then talked about wearing a pull up for shopping or anytime we were a long ways from the rest room. She accepted this because she didn't like having wet and/or messy clothes which did happen a couple of times. Sounds like your little one has better sphincter control or pain tolerance. The crying may have been caused by having a full bladder. You could include feeling better as a part of your discussion towards using a diaper or pull up.
Frequently, I could bring my granddaughter around to doing something she didn't want to do by talking about it with her, listening and responding to her thoughts. Sounds like this is your style too.