Once you give them a "loan" you should be able to give her an EFP as part of the "loan payments," which she takes immediately. (Technically you give it to Thomas since you go to him to collect the "payments," but Jenny gets hold of it immediately.)Now that sex is a anytime thing (no dice games), there is no option to give her a potion any more.
Plus, her chance of impregnation now increases after each kid she has (+3% each, capped at +30%).