if you witnessed a tie (or several) then assume she is pregnant... and start preparing Everything you will need- it is a long list! signs vary from girl to girl- one of my girls doesnt show any signs until a week before the birth, and her daughter doesnt suffer well- and complains from like week 2!
how old is she? this could have an effect on how she copes, as well as her size?
there is a breeder talk section here, further down the forums page- you will probably get more responses posting there?
oh, and hello and welcome to yorkietalk- you'll learn a lot here!