Chihuaha and Lab mating

Question
My baby girl chihuaha had her first heat a little before a year old.  We also have a male lab outside that is not neutered.  After her "period", my mom saw her on top of our lab and now her nipples are very swollen, her vulva is still swollen, and she is urinating very frequently.  I've read about false pregnancy's, but my question is there any way possible way that our lab could have gotten her pregnant.  She's so little...

Answer
Hi Brandy,  Odds are against it, but if somehow it happened, you need to get her in to a vet and get an xray to make sure the pups don't get too big as it could kill her.  She probably has a false pregnancy, but I would play it safe.  Hope this helps,

Dawn