I'm undergoing training sponsored by my company, along with a few other colleagues.

All of these people are new to me. One of them, a girl, has been cause of nagging annoyance for more than a week now. (It's been two weeks into the training. Two more to go)

At first, she would occasionally clarify doubts from me, instead of asking the instructor. I didn't mind, because the mistakes she made were lessons for me too.

But she's taken my complicity to mean something entirely else.

By the end of the first week, she basically doesn't bother following the instructor, fumbles along knowing I'll help, and when she does get stuck, she'll disturb my flow of work (it's coding, and you do need to think. I can't think while yapping with other people. I need my focus and concentration.)

She has started doing it very frequently now. She often follows up the interruptions with remarks like, I trouble you a lot, don't I?
Or her pessimistic, lazyass pov: she doesn't understand much during training, doesn't want to work to understand it, but will readily blame the instructor and her non-programming background for her impotence.

That's exactly the attitude I detest.
I have been programming since I was in the eighth grade, so to me it has always been my first love

She has annoyed me to the point I dream of shouting in her face to ing shut up and let me be for once.

How can I tell her off without burning bridges? How can I best handle this?

Can you nicely tell her since this is all new to you, you really want to concentrate on what the trainer is saying so that you can effectively do your job. Or maybe you can suggest she go ask the trainer since that person is much more knowledgeable than you are. Whatever you say to her if you say it nicely and it burns a bridge, that's on her and not you. And sometimes burning a bridge is not a bad thing.

You are not her first rodeo.

It is far more likely than not, she has leaned on co-workers more than what is polite, or necessary. She chooses to bother you because she won't look like an idiot in front of the instructor for asking too many questions (as she isn't sounding very competent from what you have said).

It is important for you to realize that you will run into people like this, in every workplace, classroom, learning environment. It is not her that is the problem here, it is your inability to assert yourself properly to stop these 'assaults' as I frequently refer to this type of person.

If you cannot sit elsewhere in the room, then you must deal with her. At the beginning of the class when things are getting settled to start, simply tell her you would appreciate her not asking you to help her any more. You do not owe her an explanation, nor do you need do anything else when she tries to figure out how she's lost your 'services'. If she kicks up a fuss, repeat, "I would appreciate you not asking me to help any more". Then get back to the business of doing your own work.

You will find that when you put a stop to behavior that she has shown toward you, and put a stop to how you have responded, the tables have turned, and you are free from this emotional burden.

Getting angry, shouting, arguing, 'telling on her', etc. will only feed into her lazy victim role, that likely serves her well, and has for some time.

Keep it simple and straight forward and repeat if necessary.

You are the only one who can control what behavior you are willing to take from anybody, and it is totally in your control to stop it.