I have a very sml. 3 mnth old puppy. I dont want to harm her w/chemicals. What can we use to rid her of fleas?

She is so small in size. I am worried she will have ill affect if we use something to powerful. She is part Shiz Shu and possible Corky. She looks more like she is only a few weeks old rather than 3 mnths. We have bought her a collar but I am affaid it will cause skin irritations. Please help. I have a photo I can share of her so that you can a better idea how big she is. Thank you!