I wish i didnt tell my boss i am pregnant,..

So i am 18 weeks. I told my boss 4 days ago that i am pregnant. She took it well.. a little too well... we do not get along great and i thought hm, weird shes so ok with it. Anyway, today she emails me about something that i supposedly did wrong 3 weeks ago and that was i filled out a timesheet incorrectly (i do not recall!) and i dont get why she didnt mention it till now..... anyway im a casual she wont put ke on permament. im way past the probationary period and have been working there 9 months. I strongly suspect she is about to sack me... can i go for unfair dismissal or if she says its for poor work performance i probably wont have a leg to stand on will i? just funny she only starts to complain after i announce my pregnancy