Remember my last, Petunia!

[Anastasia]

No: HPFGUIDX 107158

Anastasia:
I just read over the passage with Petunia getting a strange howler 
many of us wonder about.

"It's [the Howler] adressed to ME, Vernon, look! [followed by exact 
address]" 
"Remember my last, Petunia!"

Well, if you happen to get a letter dropped on your head with your 
name and address on it, what do you suggest? Right, that the content 
of the letter is meant for you. Then why "Remember my last, PETUNIA?"
The speaker seems to be familiar enough with Harry's aunt to call 
her by her name only. DD seems not to be the man to do that if he 
didn't know her well enough. Does he know her that well?

As far as I can remember, DD admits to have SENT the howler. But 
that doesn't mean that "my" refers to him, does it?

You see, I'm very confused. I just cannot come up with any decent 
theory of a person calling Harry's aunt "Petunia" except of... Lily!
But what could Lily have told her? That she cast a spell to harm 
Dudley if Petunia ever harmed Harry? Some prophecy?

HELP!!!!
Anastasia