From what I understand it's possible to impregnate and be impregnated by Venus. But no matter what I can't seem to trigger her getting pregnant or at the very least she never mentions it and I can't talk to her about it.
From what I can see from your save file, Venus has already been successfully impregnated--for 2 days now. She won't start showing until the third day of pregnancy, and will automatically give birth on or after the 7th day. So it looks like everything is working as intended, you just have to be patient.