Thank you for your question and welcome to Just Answer.
Your daughter is teething again with the eruption of her 6 year molars. These new permanent teeth erupt behind the last tooth visible in her mouth and do not replace an existing primary tooth. As the new large molar erupts, there is a transition period where the gum that previously covered the space becomes a flap that covers the new tooth. This is perfectly normal ans will disappear as the molar continues to erupt. An itching sensation is quite normal. The more your daughter eats harder foods, the quicker the flap will disappear. I hope this answers your question.
If you have any concerns regarding this issue that I have not addressed, please let me know and I will get back to you with more information.
Sincerely, XXXXX XXXXX DDS