Ensure she goes to reputable puppy classes, try to choose from www.apdt.co.uk or www.puppyschool.co.uk . You don't want any where there is boisterous, free for all play, pups need to interact off lead but this should be with carefully chosen pups within the class Book up quickly as the spaces do go fast usually.
Bad puppy class is worse than no puppy class.
Lead walking - practise plenty at home, use food treats to lure along at first - as the chi will be tiny, you can use perhaps some tasty treat smeared on the back of a wooden spoon to avoid bending too much!
Puppy class will give her confidence with other dogs and give owner support too - if she meets other dogs beforehand, perhaps keep them on lead to start with, and her off lead just so the situation can be gauged effectively. If she tries to hide under a chair, let her - it's very important she comes out in her own time.
Good luck!