Just a flat buckle collar is all a boxer, of any age, requires. Or you could think about a harness, although since she's only a baby puppy you'd end up buying several as she grows out of them.
But if you want her to stop pulling, then you're going to have to teach her not to pull. There is no collar that can do that for you.
The best way to teach her not to pull is simply to stop walking any time she starts pulling. The moment she puts weight into her collar to start to pull, you simply stop. Just stand there until she gets bored and either sits down or looks up at you. It won’t take her long to figure out that she doesn’t get what she wants (which is to get wherever she’s going as quickly as possible) by pulling. Instead, she only gets anywhere when she walks nicely.
Now, this isn’t a quick method. The world is an exciting place for a young puppy and she’ll quickly forget herself and start pulling again. LOL – after the first “halt” you’ll probably get about three steps before she starts to pull again and you have to stop again. But it *does work*. It actually teaches the dog what it is you want, and that they have to comply in order to get their walk. Devices that claim to stop pulling don’t teach that – they simply make pulling unpleasant. Take the device away, and you’ve still got a pulling dog because it hasn’t been taught not to pull.
In fact this is an ideal time to be teaching her – many people get to around 6 months before things have got so bad and they start trying to teach their dogs to walk nicely. But an 11 week old baby does not need (and should not have) exercise by walking. So if it takes you half an hour or more to get around the block, that’s actually a good thing and she’s learning about how to walk nicely into the bargain.
If you do a search of the forums, you’ll find plenty of previous questions and advice on how to teach a dog not to pull. Some will discuss harnesses and head collars (halti, gentle leader, etc). Obviously, you can’t put something like a gentle leader on a boxer puppy – I don’t think they come small enough. But you could buy a small dog harness if you prefer. You’ve still got to teach her not to pull, of course, whether you stick with a flat collar or you use a harness. And the stopping method described above is generally the best way to do it. Good luck.
