My dogs tied is she pregnant?

It's likely. We count gestation from the day of the first tie since that usually does it unless there is a problem somewhere. If it was unplanned you can speak to your vet about the mismate shot and it's risks (such as pyometra, generally leading to a need for emergency spay) or a spay and termination which is usually preferable. There is an additional fee for the spay but still much less costly than continuing with a pregnancy and rearing pups properly and all the vet bills that tend to crop up.
If you want to continue with the pregnancy you will confirm the pregnancy at the vet in about 3 or 4 weeks and begin the rest of your prenatal care. It's also a good idea to begin putting money to the side now for all the pre and post natal care, emergency such as c-section, illness, standard maintenance and check ups and all the other vet bills that tend to crop up. There is more basics information and detailed links for you in the links. Good Luck.
q3525724.html#a2810229
http://www.woodhavenlabs.com/breeding.html
q3388198.html
q2722771.html#a3046267
q5762034.html#a2906893
q8997030.html
http://www.wildheirlabradorrescue.org/readingroom/what-is-a-back-yard-breeder.php 
http://members.tripod.com/antique_fcr/goodbreeder.html 
http://www.wonderpuppy.net/1breeding.php
http://www.petfinder.com/index.html