https://youtu.be/Q9W7pvOLxmQ

Besides what everyone else has said, she was also having issues with space sickness and the station was more stationary and caused her less issues.

Terry Farrell wanted to be a recurring character in DS9, she just didn’t want to do it full time anymore. When her contract period came to an end at the end of season 6, and no one approached her about renewing it, she decided it was her que to leave. But instead of having her leave the station, they decided to just completely kill her character off. I feel like she may have well stayed seeing it was canceled in the next season.