According to this and other news articles I've read, she had been battling breast cancer for the past ten years and passed away in her home about a week ago. Fifty is pretty young, but the cancer sadly provides an explaination to her death. She also had a role in When Harry Met Sally, a few guest star roles in shows like Full House and Who's the Boss and had a few albums out, including some broadway songs.
This is really sad news. I have seen the first two Swan Princess movies. I haven't seen the third one yet, but they were a nice guilty pleasure for me and I did like her voice for Odette. I hope that she is at peace now and that her friends and family members will be able to get through this emotionally difficult time.