The idea is that early on in the game after their first dungeon crawl Vicki comes across a jeweled pendant unaware that the ancient necklace is called The Eye Of Mesgedra and inside the jewel holds the soul of an evil dragoness Mesgedra. The jewel has a corrupting influence on vicki feeding off her insecurities and anger. depending on the path your on and the choices you make vicki may be overwhelmed by those feelings and become transformed into a massive fire breathing dragon and storms off in a rage. after she calms down As a dragon Vicki at first finds it incredibly freeing, to just be so powerful and fly thru the clouds, however her her transformation caused some damage at the village she was in which causes a panic, a true real dragon of Vicki's size hasn't been seen in centuries and it causes the summoning of knights and warriors to come and handle the situation which only enrages Vicki causing her to become more corrupted by the eye of Mesgedra making her more powerful and villain like.
depending on your choices, Vicki can be saved breaking the spell and turning back to normal. you can save her and she remains a dragon but is in control and not as powerful or you give into the thrall and vicki becomes The Dragon Empress and conquers both worlds bringing forth a new age of dragons.