Love, love, love this Petunia. I love how you start with the angry, embittered woman we see in canon and then open her up to make her seem a living, breathing woman.
When she first sees Snape at the graveside, one has an inkling, of course, of where the story is headed, but the way you develop the relationship over time is fresh and totally believable.
The addition of Wesley and the food is also a wonderful way to develop character and reveal emotion without resorting to fusty narrative.