Interview with current employer ?

I work for a home hospice agency as "PRN". While I have been a PRN I have actually managed a case load my entire time of employment (1 yr) and worked PRN, nights, weekends, holidays etc. Recently I interviewed for a part time position at my work, doing essentially the same thing, but instead I would be working half of what I do now.

During my interview and afterwards, my boss indicated to me that she is not sure I could handle the position.... I don't really understand this comment, since I have been doing double the amount of work, effectively for over a year. It was a pretty big slap in the face to me, because my boss has always told me I'm doing a good job (even when I may not think so). Then in one interview, she undermined everything she has ever told me.

After this I have begun to explore other options. Quite honestly, I felt taken advantage of that I had a higher caseload then the full time, benefited employees, which is one reason why I wanted to interview for a position with benefits. The comments made towards me, only has pushed me away more. It's almost like I'm almost being punished for recently discussing my concerns with my conflicted role. I am completely fine to be told I was not chosen for the position because there was a better candidate. But to act like I can't do it when I've been doing it and then some for so long, is completely different.

Any thoughts?