I think the problem is not telling Rumple but Henry, who will be on Rumples right. I mean she will want to talk with Henry alone or in Storybrooke with her mum. This bombshell will be big for her and she have to take a while to sort everything out. She lied to Henry and told him that his father is dead and a hero and know he is the son of the Dark One, who threat him a while ago. From Hero to the devils son, how should she discuss it. She will maybe think that her whole existens, her love for Neal and her son was all part of Rumples plan. Of course she will not be open a first, specially with Rumple, but I don’t think that she will try it to hide only take her time to think for 1 or 2 days.
Heros don't get their Happy Ending!