Cold symptoms are not symptoms of herpes. Period.
I know you are worried about your grandchild, you love her very much and would be devastated to hurt her in some way. But the symptoms that she has have nothing to do with herpes. Twenty days is too long for transmission.
I don’t think your daughter should start doing things like checking in her mouth. That would just cause her to be confused, I think.
You need to remember that in all of her little life, there will be others will cold sores that will be around her. This is a situation that just is. And not everyone will be so cautious as you. You are likely the least likely person to infect her!
If you need more reassurance or want to ask another question, please write back to me.