There are differing opinions on this. Just like there are those people who are pro-life and there are those who are pro-choice in humans, the decision to spay a pregnant cat is a personal one best reached by first examining the facts (pet overpopulation crisis, unknown heritage which may or may not be capable of producing viable, healthy kittens, unknown medical history, etc.), digging deep to determine what is the best choice for the cat in question (risk factors including age and current health status) and then to attempt to provide the best possible outcome for the cat ~and~ the owner (financial responsibility for the cat and kittens until suitable homes can be found, time involved actively caring for and raising a litter of kittens to name a few things which should be considered).
Many people tend to place human characteristics on their pets - this is called anthropomorphisizing (that may not be spelled correctly *sigh*) and it isn't fair to our animals. They do not concern themselves with the politics of "our" society. What seems right to us may not always be right for them. As the sole guardians of our pets, we must weigh each and every factor involved and then decide what is the best course of action for our ~individual~ pets and circumstances.
Best of luck to your friend in making what can be a difficult decision. I hope she will come to the right choice for her cat quickly and effortlessly.