Dog Used to be, but Now isn't Friendly w/ Visitors

Hi there,

I have a 2 year old female English Bulldog, who is newly growling at visitors to my home. She used to be just OK, but now that I have a new puppy, she must think she has to be more of a protector.

Anyways, she growls at people coming over. I have been having the guests give her treats and then pet her, which she accepts. But her inital response is to growl. Then after/if she settles, she may be OK, but then they do something to startle her and she growls again.

How do I correct this (i.e. do I have people give her pets and treats) or do I give her a firm "NO" when she growls (which isn't working, anyways) or put her to another room altogether?

Thank you again.

Has she been spayed?

Yes, she is spayed.

She thinks it is her place to keep the house safe. You need to teach her that it is not. This house, the puppy, the people and she herself are all your responsibility - not hers.
So you need to work on her respect for you as her leader and teach her proper manners when we have visitors. When she is feeling insecure about someone new in the house her natural response should be to look at you for advice - not just act independently.
Keep letting her have positive experiences with these people, but also correct her bad choices of growling. If your corrections are not changing her behavior it is because she doesn't respect you. It doesn't mean that you have to be harsh or mean, just more consistent and clear throughout the day not just when you have guests.
Also giving her lots of things to do - good manners when people come over - takes her mind off of them and on to her jobs. This also causes her to have a chemical outpouring of calming chemicals that make her more agreeable over all - as opposed to the adrenalyn rush she gets when she is nervous which feeds energy in to her fears.