If your basset is not nuetered and your yorkie is obviously not spayed~of course there is a great possibility that she is pregnant. Please for the sake of your little girl get her to the vet immediately for a spay. It can be done even if she is pregnant. There is no way that she will be able to survive a whelp of a mating between with a basset.
__________________ “Never argue with a fool, onlookers may not be able to tell the difference.”  Mark Twain |