She may not be growling in aggression. It is hard to know because we are not there to see her behavior.
This behavior should not be tolerated. Absolutely do not pet her while or after she growls at you. Remain at the top of the stairs until she stops growling, and then come downstairs.
Wait to pet her she has stopped growing for at least five seconds.
Sometimes they don't mean it aggressively. My grandpa had a dog who would show her teeth at everyone, but she was the sweetest dog and never tried to bite anyone. Still, I do not think it should be tolerated whether it is meant aggressively or not.