well im not sure then. but maybe do actions with bianca that increase her arousal/love. i forgot the exact amount i had when i pregged her but if it doesnt happen soon then there is a possibility that its a bug or you just dont have patience. or that Mr. FarmGuy just set the bar way too high.
Well, i tried to help i have absolutely no idea. Good Luck trying to figure it out. but in case this helps. what i did was every day (in game) banged her on the living room floor and came inside her every time.
It aint about patience I have played literal days trying