Uggggh

My daughter who is 3 has a fever blister because she is sick i have a 1 month old who I'm extremely worried about getting the fever blister im making my daughter wash her hands a million times a day and basically not letting her around the baby! How can a baby get it? Is it that easy to catch like i see stories about babies getting it and dying but how easy is it to actually catch?? Her blister is almost cleared up