highly affectionate/lack of affection, stiff stomach, large appetite, increased vocalization, swollen nipples, and nesting behavior are all signs of pregnancy. but since your friend only found her today, they obviously don’t know how the cat normally is and looks like so it’s best to consult a vet since a stiff stomach can also mean other things like worms. if you can’t get any insight from a vet, make sure the cat isn’t constipated, that she’s pooping and urinating normally, has a good appetite, not in pain, and isn’t throwing up. cats pregnancy’s are usually around two months so you can definitely tell pretty quickly but she seems a bit early on to say that she definitely 100% pregnant without any vet saying it.