i totally agree with cali's advice... and NILF is good all around training in general for any dog...
i have had a similar experience with my rescue dog, and it takes a lot of persistence, but you can help her to overcome these issues...
as far as the snow, i've had similar issues with it where i live, luckily my dog absolutely loves to run and roll around in it! we do play some indoor games for exercise also....
one thing to add to what cali said... you cannot give her too many treats in these situations... i always made the mistake of backing off on the treats a bit too soon, i buy all sorts of stuff for my dog for just this reason (definitely account for it in her diet tho) and have tubs of them all over the house, my pockets almost always have something in them, and my purse (it is a little embarrassing sometimes!)
you may also want to try visiting petsmart at other times for a while, maybe ask an employee when they are the least busy... bring tons of treats, and ask everyone to give her one... that way it will hopefully be a bit less intense for her...
oh, and please keep us posted on how you are doing...