Ginger's information was spot on. If the father of the puppies was a larger breed, you need to contact the vet immediately to let him or her know that you are expecting puppies within the next 48 hours, and that you may need them at a moment's notice to do an emergency C-Section. Please keep us up to date as the weekend progresses, and PLEASE post pics when she has the puppies!
Ghilly
At 61 days she is more or less ready to give birth! You will be able to tell when the birth is about to happen if from now on you take her (anal)temperature twice a day. Normal temperaure for dogs is around 101 degrees, can be a little more, can be a little less. What you are looking for is a sudden drop to 99 degrees or around that mark. You can safely say the birth will occur within hours after that. She may refuse food, she may go "denning", she may vomit, or even start to tremble a bit as the labour pains begin. All that would be considered normal, so long as she didn't get dehydrated, and the symptoms at that stage were not extreme.
It sounds pretty normal for her to be large in the belly at this stage. So long as she is generally fit and well, eats ok, pees and poops ok, and there appears to be nothing else wrong with her, then it is most likely OK.
BUT ....any doubts AT ALL, take her straight away to the vet, or if possible, call the vet out to visit you.
I guess you are all prepared for the birth?
Was this a planned birth? A thought-out breeding? And do you know who the father of the pups is? Is he the same breed and similar weight to your girl? If not you could be looking at real complications during the birth, and my advice would be to seek out the vet's advice right away.
In fact, if this is a "first time" for you and her, I would say definitely get the vet's advice PLUS assurance he will be available for a call-out if needed during the birth. Put that number on speed dial.
Good luck, and post a pic of the puppies (if you get time, as being a doggy grandma could be tiring!!)