what do you tell a smart 4 yr old about chemo?

Hi,   I'm new here.  My mom was recently diagnosed with colon ca, 6 liver mets.  She has started chemo and they expect her hair to thin and fall out soon.  My question is in regards to my 4 yr old daughter.  How do I talk to her about the changes in her Grams' appearance?  She knows her Grams has some 'bad germs that make her really sick' and that she has to get 'special medicine,' but I'm not sure how to proceed?  Any advice is greatly appreciated. Thanks