Responses
You are quite literally contradicting yourself with this. She HAS been sheltered and locked away by her family and her "staying at the castle to be a lady" would also be her being sheltered again. There is never a guarantee for her safety in a world like this one. She has been expressing her desire to learn and grow for (what we can assume within the timeline) at least a few months now! All Riftan has been doing is to push back and discourage her, instead of offering support. Why? Because he has a warped image of her.
Also they absolutely do need a healer. The story has made that quite clear
Classic damsel in distress. Needs to be saved by a big strong manly man. I hate it. Also, Riftan, hello, you are a commander. Did you just leave your troops in the woods somewhere and went along to search for your damsel? Welp...