WELCOME (I am in PA too)

I would not worry yet. If she is malnourished and/or dehydrated there probably isn't a whole lot that needs to come out yet. Combine that with the fact that she might be too scared yet to do her "business". And cats that have been outside for a while will probably only seek out the litte box in the dark of night, holding it all day.

After she gets a few good sized meals, it should start coming out the other end.

I would suggest, however, measuring and monitoring what (and how much) she eats and drinks.

Good luck with her. Please keep us posted.