Yep, it is a stress thing most likely - is she in kid? Not an easy one to treat I know from experience, likely to re-cur at any given time.
Treatment with combination of steroid injection and antibiotics (Betamox), also injection.
Think about it careful - it may be hereditary, or maybe not. I had to give up eventually as the continuous treatment meant that we couldn't drink the milk and it was stressing me and the goat to inject her every couple of days. She was PTS.
Sorry, probably not what you wanted to hear. What breed is she?