My 4 year old said i was lying

So today my daughter walked up to me and said I was hiding her baby brother and that I had to give him to her. I told her there was no baby brother and she said I was lying.I started crying. I missed my chance this month I am sure if it. System Thursday got peak. Saturday did the deed again today. So I think I missed it.How can I explain it to her that I'm not hiding her brother when she doesn't have one.