DontDon't forget that the only person we know is getting notes sent home is Harry, who for areour purposes is essentially a muggle born, in that his "parents" are muggles and have no access to an owl.
How would muggle born-born students receive their Christmas presents, unless Hogwarts/the student themselves usedsent their personal owl, or the school owl to their parents, so their parents could then use said owl to reply.?
Since your quotes clearly says Hedwig was sent WITH a note,
A second, very small parcel contained a note. We received your message and enclose your Christmas present. From Uncle Vernon and Aunt Petunia. Taped to the note was a fifty-pence piece.
it seems that the school automatically sent out owls to all the muggle born studentsstudents' families who would otherwise have no access to an owl for Christmas.