This is truly brilliant! I so love it when characters are kept so well in canon, but at the same time taken out of the context, looked at closely, and given a three-dimensional, realistic life beyond what we read and see. Of course Petunia and Severus would react differently with each other, and would react different under the circumstances they meet, and the reasons for that. And how very fitting that they an find comfort and consolation within each other, and with their small time-out at this special day, once a year. At first glance, they look so different from how we know them, but at second glance, we recognise it as a hidden part of them.