My emails occasionally go to someone else's junk. Daughter who is with yahoo and gmail is the one who noticed it. I am distressed about others missing messages in this way.
Then your daughter needs to start marking them as Not Junk/Spam when they wind up in the Yahoo or Gmail Junk folders. Comcast will have little to no control over the spam filtering parameters used by other email providers. The drawback to all of the free email providers is that there is no number to call in the event you need help with something like this. You can only rely on whatever support discussion forums or help files they offer.
But all is not lost----------both Yahoo and Gmail have a way to whitelist an address/sender. So your daughter might want to try this------------------