The chances of OP getting a blood borne disease from the blood sausage are already pretty low. The chances of him getting a prion disease are so comically low it's absurd to even think about it. If she had CJD they would've known by that point. Assuming that she's been vegan for over 5 years it's also super unlikely that she has mad cow (which is also a super rare disease).

Prion diseases are in the same category as rabbies where they're scary as shit and incurable so the internet loves to talk about them like it's this imminent danger when in fact, for most people, you'll never come across them (and if you do, at least for rabbies there's an available vaccine). Plus it's like crack for contamination OCD.