I liked it when my beardie didn't poop in his cage. I think he got used to getting a
bath every other day and just did his business there. Then when I built the outside enclosure he would always go there or the
bath. Never in his cage. It was great. Instead of cleaning the whole enclosure twice a month and spot cleaning almost every day I just put the poop down the drain or left it (the outside enclosure was over the lawn).
He's gotten back into the habit of pooping in his enclosure and it's disappointing. He usually does it when I'm not there and then runs around with it making a huge mess and a huge cleanup hassle. Ughh.
As to pooping in the cage all I can say is try just leaving her in there for a reasonable amount of time until she poops. If she has to be taken out for a
bath or some other reason then so be it, but leave her in there otherwise. I don't know if you can necessarily train them to poop in a specific spot though. It seems like they just go where it is most comfortable or until they just can't hold it anymore.