Is my dog pregnant??

Ok so, my dog has had 1 litter and then her daughter had a litter with the dad, I know weird, anyways the dad died and we got rid of the daughter so now we 3 little dogs and 1 big dog and we thought if any of them got prego it would be our small female but I think the big female is pregnant, and like I said she's had a litter before but that was over a year ago and I just squeezed a teet to see if she was because she was acting weird and milk came out so I don't know but her last pregnancy was over a year ago! PLEASE HELP!