Well - we always use Lopatol (nitroscantate)in pregnant bitches as it covers all the bases. Mind you our recommendation is to deworm them just before breeding, just before whelping and at 4 weeks post. So I'll give you the basics and you can decide what to do with your 30 day post-breeding bitch.
Another option would be Cestex (epsiprantel)to cover just the tapeworms.
Panacur (fenbendazole) is also a common one - they even have dosing charts for pregnant bitches. Downside only treats one type of tapeworm (Taenia) so you would need to know which your dog has.
Droncit (praziquantel) is also tested safe for use in pregnant dogs. All say they are tested on pregnant bitches, but you should contact the companies and confirm after what day etc.
The two common types of tapeworm that dogs get is Taenia (from rabbits and rodents) and Dipyldium (from flea infestations). Knowing which type your pet has can help make the decision for what to treat with.