actually Lilly Tilly you did it perfectly, the only thing that you should not have done was punish for growling because i a dog learns growling is bad they will skip that step and just bite instead. Trading is the best way to get over object guarding. I hate when people just straight out take stuff from them thinking that it will teach the dog you are boss, all it does is teach them you take their stuff if hey don't guard it. Trading lets them know when you take their stuff they get something yummy!
anyhow I think you need to broaden your socialization to include more people. You said she gets used to regulars so you have to try to get more people so she learns everyone is just as safe as the people who always come around. Firstly shake the persons hand or say hi to them and give them a big smile, the person can be a complete stranger just tell them you are socializing your dog and ask them if they would give her a treat, (this is when you will give them a few treats). Have the person kneel down (if they can, older people would have difficulty with this so they do not have to) at a distance your dog is comfortable with and holdout the treat. Your dog should take it, have the person give her one more. Don't have the person touch her yet because she is not ready for that. Do this with as many people as possible until she gets excited to see people when you shake their hands. Then after they give her a treat they can gently stroke her side, if she is comfortable with that and does not at up they should give her the second treat and you should praise her too. then you can do it with all people she seems excited to meet. With people she does not get excited with or walk up to when you shake their hands make sure they do not try to pet her but only give the treat. Work on it with people in public and people in your home when you let them in the door. Never make her go to fast. If she is not comfortable with certain people then don't let them touch her, just give her the treat.
Now something that is very important is variety. She needs to meet all kinds of people. Here we go: Hispanic, Black, Oriental and White people, people in baseball caps, people in wheel chairs, people with canes and walkers,older people, adults, teens, toddlers and infants (not until she is very good should you do the last two) of both genders, people with different length hair, men with facial hair of all lengths, people with different accents, people with high heeled shoes and boots, people with big winter jackets, people with snowpants, gloves and winter hats, with umbrellas, deep voices, people with casts on,run of the mill people who are just dressed in sneakers a tee shirt and jeans with no hat or big cloths, and what ever else you can think of. Also make the people greet her in different ways later on when she gets good at this. Have them lay down (people you know not strangers
) and sit or stand or bend over her (once she is comfortable) She'll need to get used to some childish movements (although you are to protect her and make sure kids don't do anything to hurt her like pull her ears or tail, it's also best if strangers NEVER try to pick her up or hug her) and high shrill voices. It seems like a lot of work but if you bring her to as many places possible (pet stores, parks, trails in the woods, beaches, play grounds if she's allowed) you are bound to run into all these people, plus you can stage some of them with your friends and their families.
If you are having people over and you do not think it is an appropriate time for socializing or she is not ready to interact with people for a long time in her home then I agree to crate her or put her in a room with toys to entertain her.
Good Luck and keep us updated with your progress!
Oh and if she is in a situation and growls i agree you should remove her from the room (no, "oh it's ok hunny" just take her out of the room and put her someplace alone.)