Is it normal my prank totally backfired on me

so their was this office manager where I am a asst. ceo at my dad's company who had a huge stick up her butt.I tried a couple little pranks like calling her a glorified secretary, telling her she no longer gets a break and I was taking her desk. She just looked at me like I was a dumbass. I decided to pull out the big guns and tell her she was fired for insorbination.She really thought it was true and has been told she can return back but she is so mad she won't. It's been a month,The place is falling apart, my boss is close to having a nervous breakdown and clients are furious we fired her because they liked dealing with her better than me and she was there 40 years. Even my dad is mad at me. I never had anyone take my jokes seriously. What do I do?