USED!!!

I feel so used, My DON brought in a new nurse, finished nsg school with an RN, bu t got married and stayed home for 10 years and just now wants to begin her career...
I was instructed to help her learn the ropes (she needed everything to be taught to her- BP's, Insulin shots, IM's, IV's, assessments, careplans, dsgs, sterile technique, EKG's, foleys, etc. etc and I MEAN etc. All this at the expense of my regular work.
Two months into it, and its taking a lot of work, she announces a pregnancy ( she was 5 months pregnant when she announced it) and reduction in hours,
she gave birth a month ago and now tells us that she is not quitting but is not coming back to LTC- not because we weren't good to her, but because she wants to move on now that shes got the hang of things...
I feel so USED!!! I put so much into teaching her and she wasn't easy - required a lot of encouragement and practice!!! If she would have stayed a year, I'd feel at least we got something out of it, but we just got 6 months, and most of it was one to one tutorial in nursing!!!
According to my boss, there is nothing we can do- legally she is in the right, when I tell her we should have stipulated a two year contract if we were reeducating her, but my DON disagrees.