At 11 weeks old, your job is to socialize her and build her confidence. That means introducing her to lots of new things (but not overwhelming her), and teaching her that the world is fun, good place! This includes teaching her that strangers are nice.
Asking how to create a protective 11-week-old is like asking how to prepare your 6-year-old child for the Marines...they're so young, you need to be teaching them the basics now and not worry about that advanced stuff so much (unless you are serious about wanting a protection-trained dog, in which case see the poster above me's advice).
Barking at strangers isn't a good thing. If she's barking at them to tell them to stay away, she's most likely reacting out of fear or uncertainty, not protective instinct (again, she's a baby--she's not developed enough to be truly protective yet), or is trying to get them to play with her if she's very friendly (in which case it's not so dangerous, but still bad manners). Even if she is extremely precocious and is truly being protective, it's still not a good thing because you're not in control of it! You don't want a dog that feels the need to "protect" you (or more likely herself) from visitors to your home, harmless passersby on walks, etc., and that is where barking at strangers tends to lead if encouraged.
If you want to be able to count on her protection, the way to guide her is by finding a trainer who knows how to do that training. It isn't something to mess around with on your own, as you can easily create a dangerous dog (as in, one who will bite even when you don't want them to), and you also won't be able to count on her--she may be aggressive on the surface but when push comes to shove, she'll run. Protection training involves a lot of mental preparation for the dog, as well as testing the behavior to make sure the dog actually will do it reliably.
Otherwise, simply building your relationship with her while building her confidence about the world around her (including people she doesn't know) is the best thing you can do for your dog.
I throw this out here a lot, but I think it's a good example--one of my dogs actually did protect me from someone who was trying to hurt me. This dog is also super friendly to strangers, loves everyone, and is generally just the nicest dog you've ever met. I've never seen him bark or growl at someone, except the day he latched onto the arm of the guy who was trying to hit me and wouldn't let go until I pulled him off--and the next day he was right back to being his friendly, outgoing self. Being afraid of strangers is always a bad thing! Being confident and having a strong bond with their owner is the best situation for a dog overall, and the most likely one to set them up for protecting you--though of course it is a gamble unless the dog is protection trained.