I don't think she was mad at you necessarily but she is only a baby and she is learning about proper and improper behavior. It shows spunk and personality and that she has confidence in herself, youand her surroundings that she growled. It is normal.
Keep doing it frequently and she will get accustomed to it. You should yell "ouch" really loud if she tries to bite you as that is not acceptable.
My Baby Ava used to growl whenever I brushed her but now she is so good and actually like sto be brushed because she gets treats and "love" when it is time to bruch her. Sometimes she gets so relaxed she almost falls asleep.
You are doing fine, just remember she is still very young.
