I need advice please

I'm married and 28 weeks pregnant. I'm a nurse and my manager is an extremely terrible person. She punishes everyone to the extreme if one little thing happens. She apparently thinks I'm not good at my job and is trying to get rid of me. She has me on a 90 day "improvement plan" During this improvement plan, which is almost over, we had meetings to discuss how I'm doing and never did she have anything bad to say. (Proves my point that I'm not a bad nurse!) But one day she made me go into her office and she said that something happened and I'm not being consistent with doing well. I argued the fact with her because it was the end of my shift and I was giving report to the next nurse when an aid came to us and told us about a patient situation, so what happened was the next nurses responsibility to go and assess the patient because my shift was over. But somehow I am to blame for this..?! She just clearly has it out for me and wants me gone. Like I said, I am 28 weeks pregnant so what am I supposed to do if she fires me? I won't have any insurance when my baby is born. I am freaking out :( And HR is absolutely help at all. They dont do anything about it. A lot of people on my unit complained to HR about her and nothing ever comes out of it. I don't need this stress...it's not good for me or my baby. What am I to do? :'(