Was I wrong or is my job just mad they screwed up?

I'm 32 weeks pregnant. I work as a caregiver and my specific client keeps falling and I have to pick her up and it's really straining my body. I decided that this will be my last month working. I told my boss beginning of August and she pretty much just said kk. Now that September is ending I looked at my schedule and new clients have been added. I went back to my job and basically said "hey remember this is my last month" my boss was livid saying why are you just now telling me this?! But I know I told her cause I rehearsed what id say for like a week straight. I offered to work until they find a replacement but shes still really upset and even hinted to not put her as a reference for my next job. Not sure what to do. Maybe I should've put it in writing or something??