Potty training is 3 fold:
first they attain ability for pee.
Then poop.
Then, night-time training, which is a whole other "ability" and night-time dryness 'ability' is usually attained even up to 7 years old... and they will still have night time accidents. Its okay.
Going poop, is usually not attained at the same time as going pee. These are 2 different time-lines and abilities. It is COMMON that a child will hide and poop... whether it be in the diaper or underwear. The more pressure you put on them to poop on demand or in a toilet... the more regression they will have.
Just go by her cues. Don't worry, she will get the ability for it... just not yet. Even adults, will not poop if told to... unless they really need to and go themselves. AND many adults will NOT even poop at a public restroom... and will only poop at home. So....
One thing you do NOT want to do... is make pooping a "problem" whereby the child will start to "withhold" their poop and avoid going altogether, whether it be in a diaper or underwear. IF this happens, then the child will have constipation problems... and this is a WHOLE other issue and problem. Many toddlers, at this juncture, get constipation problems because then it becomes an emotional issue and they will avoid going poop altogether, and it will cause pain upon voiding when constipated.
My daughter went through that and even had to see a Pediatric Gastroenterologist... and he said MANY toddlers get this problem... because pooping becomes a painful thing for them once they start to withhold going to poop altogether.
Just ease up.... pooping in a toilet is a whole different "ability" and timing, for a toddler. It is wonderful she does go pee... so bravo for her. She will poop in a toilet when ready. As you see, no other punishments or rewards will work to "MAKE" a toddler go poop in a toilet. They will do it when they are biologically/emotionally ready.
Just let her know she is okay and fine and you are proud of her... nonetheless.
And keep in mind, even once they ARE potty trained, accidents will STILL happen. And this is normal and fine. No biggie. Even adults can have a hard time holding their bladder.
I would also recommend a potty for the car. Like an "On The Go Potty" for example, or a travel potty. Which you can get from www.amazon.com
For us, it has been a lifesaver for our kids, while we are out on the road and they need to use the bathroom, when there is no bathroom nearby.
All the best,
Susan