Take her along to a vet and get her checked over for any medical problems. Since it seems to have occured so suddenly, a medical problem should be looked into first (and it could be a UTI still).
But if none of the above apply, I'd be inclined to suspect it's a behavioural thing. And I'm not meaning "behavioural" in the problematic sense that you've got to get help with either.
A great many puppies do what is known as submissive peeing - happens when they get over excited, and usually when someone comes home or someone new visits. And it often happens around about your girl's age - since pups go through their second fear imprint stage around then. So that could possibly be what's going on here. If you think that could be it, then the thing to do is primarily ignore it.
Take appropriate steps such as having people ignore the dog when they first come over (you can warn them they'll get their shoes peed on if they don't cooperate LOL) so that she can settle herself down before any greeting goes on. Taking her out to pee before company arrives is worthwhile too (though not foolproof). And ignoring the pup, giving her time to settle down before saying hello, when you or other family members arrive home also is a good idea.
But don't make a fuss of the incidents. Do what is reasonable to try to avoid them (as above) but if it happens, making a fuss (including trying to reassure her) just makes it worse. It's largely something you just have to let pups outgrow.
