If you can get it TOMORROW, see your Dr. or clinic and get some Zovirax.
Nothing helps once they start to go full-blown.
But, at the first sign of tingling and redness, Zovirax will do the best job of stopping and curing these.

Yes, it might be expensive. But that isn't a real issue... it is def. worth it!
I believe it is Rx.... I don't think it ever got approved for OTC.
You could call your pharmacy and ask.
Also, if you have any, or can get some right away...
She can/should take good doses of L-Lysine.
If she, or anyone you know, is bothered by frequent cold sores, this is definitely known to help take care of the problem. My husband knows from experience. As was prescribed by their family doctor who was a friend.
We also use a baking soda and peroxide toothpaste (recommend arm and hammer) And this seems to help greatly with cold sores and canker sores. I have had a few of those... but haven't been bothered since switching to a good baking soda and peroxide toothpaste.