Yikes! We have to be very conscientious about socializing our Filas, as they are bred to be distrustful of strangers and also to use initiative and judgement about threats, but I've never had to deal with it in a small dog. For the Filas, we start out when they are young, taking them into social situations and reassuring them that things are "normal" and okay and there are no threats, reinforcing this with plenty of praise and physical contact. We never force our dogs to accept petting or unwanted physical contact with other people, though, just tolerance and disregard for non-threatening people and situations.
You don't say how old your Papillion is, but she is probably nervous and afraid around people who aren't her family. She may need to be reassured a lot, and taken out for walks where she will have to come into contact with different people. Praise her lavishly for good behavior and correct her for unacceptable aggression. Bear in mind that she may be a shy little dog and never have any desire to interact closely with strangers, or even people she doesn't live with.
Please resist the temptation to let other people give her food and treats to make friends with her. You don't want her to take something from someone who might want to poison her for some perverse reason. Although your friends won't do anything to hurt her, she won't know the difference when it counts. If she only takes food from you, it could save her life someday.
Your vet might also appreciate it if you bring her in every week or two to be weighed and handled so when you have to bring her in for a real vet visit it won't become dramatic for her or the vet and staff. Normally, a vet not only won't charge you for this, they'll thank you for it. They don't like to be bitten, either!