If I were you I would probably also feel extremely upset. But as I'm looking at this from the outside, I'm thinking perhaps you can try to talk more with her about this?
She said you have to finish in 2018, so still not for a while. I wonder if there could be an explanation or reason for this. Maybe as runcible spoon suggested something to do with insurance. Or there could be all kinds of other scenarios I can imagine. E.g. a family member has suffered a serious illness or disability which changes her long term plans and she decides to retire early to be a carer. Or the boss of the clinic where she works has just announced that the clinic will be closing in 2018 ... I am just pulling these out of the air, but there could be many possible explanations which don't necessarily mean that she was deliberate lying before, but that there has been a very serious change in circumstances. I certainly think she owes you an explanation of why she said that, and I think it would probably be really important for you too, otherwise you will always be left wondering what happened and why she changed her mind.
I wish you all the best, and sorry that this is so hard.