The picture is hard to see ...How old is she? Is she a FF? She does not look like she is heavy bred at all...her udder looks thick but not any where near close to kidding....a little trick I learned here is ... If her little pee is pointed down then she most likely is bred....if its tipped up then she is opened..its not full proof but most mine were correct : )
If she has been with a buck then unless she is not fertile she is bred... A simple blood test will tell you if she is and about how far long she is
How long has she been with the buck? The udder will begin to form at 1 to 1 1/2 months prior to kidding.
Here is an answer to your question:
When you feel her udder area, you should feel a pouch, it feels like a very small water balloon, cupped in your hand, when just starting to fill.
If there is nothing forming, it will feel flat , no pouch. Hope that helps.