Due date vs conception

hello, so this is random but I need advice. my cousin died June 25th. His girlfriend comes to us in Septemeber and says she's pregnant with his baby. she sends us fake sonogram photos and I found them online. All the sudden, she says she's due April 20th bc the baby is small. if you do the math that means she got pregnant late July. my question is, would a doctor really push you back that far? This can't be my cousins baby... She has a tiny belly ... but if she really did get pregnant by my cousin she would be due March 17th. This has to be someone else's baby.