kellybug,
You can use pyrantel pamoate starting at about 2 or 3 weeks old. When you go to your vet visit, just tell them you dewormed her with pyrantel pamoate, they will probably advise another dose at 2-3 weeks after the first dose.
Just look for pyrantel pamoate as the active ingredient, and then follow instructions on the box... you will have to weigh your pup too.
They will probably do a fecal to check for any other worms too, at your vet visit.
Even if a mother checks out worm free before breeding.... There are dormant larvae in the tissues of most adult dogs and these can be activated during pregnancy and then migrate to the fetuses in the uterus and become active infections.
This is still no excuse for a 5 week old pup to have worms..this pup should have been treated by the "breeder". Why did you get a pup at 4 weeks old? That is really too young to be away from her mother.
It is really important to rid your pup of these worms soon!