I'm going to back up just a little bit. She's barking and reacting at big dogs because she's afraid of them and trying to drive them away. Go very slow with her, don't force her to be around them, play with them, be near them, etc. Don't spank her, hit her, or punish her in any way - she's afraid, and punishing her won't make her any less afraid. (Think of it this way - I hate spiders, and throwing me into a room full of them, and/or hitting me every time I shriek cuz a bunch of them are all around me may shut me up for a moment, but won't make me any less afraid of them!). It will only make her fear you - and other dogs. Oh noooo, a big dog, it's scary, I've got to get it away FAST or I'm gonna get hit barkbarkbarkbarkbarkbark (smack) bark barkbarkbark (smack) .... and the big dog is still there, and she's still scared. Now she has even more to be scared about .... she see's big dogs and worries about what they might do to her, plus she worries she'll get spanked by you when she sees the big dogs. Big Dog = Very Scary (not just scary).
Don't just jump head first into trying to train with the clicker, esp if she's afraid of the noise. You want that "click" to become special to her, not a scary noise. Don't ask anything of her right now. Just "click" and give her a treat. Click - and treat. Click - and treat. Over, and over, and over. And if it's just too noisy, try putting a little cloth over it, it will muffle the sound a bit until she's used to it. You may want to watch some videos on how clicker training is done before you try it - the 'click' is used as a marker for yor dog, telling your dog the instant he/she has done exactly what you're looking for, and it's ALWAYS followed up with a treat. If you search, there are many threads on clicker training, you can get loads of info here on the forum.
Also search thru and read different threads on aggressive dogs, reactive dogs, words like that - there are also loads of threads and you can find out all kinds of helpful info, lots to read. Southerngirl posted links to great videos, esp one on aggressive dogs - that one started on page 3, be sure you go back to page 1 and start at the beginning.
There are a lot of us here on the forum with reactive dogs (waving hand here), so we're all here to help you. They do need our patience and understanding tho - they have fears, and we, as they're protectors, must be their biggest advocate at all times. We can never place ourselves into the position as just one more thing they fear.