Petunia's Howler

[thehighinquisitorofhogwarts]

No: HPFGUIDX 70868

I haven't seen mention of this but what about Petunia's Howler?  Why 
was she not portrayed as being shocked, like not knowing what one was 
rather than horrified at having gotten one?  Also, how was it she 
seemed to recogonize the sender, via the voice as she immediately 
understood the cryptic message?  If as we have been lead to believe, 
Dumbledore's only contact with her was the original note depositing 
Harry at her doorstep she would not have made as readily a connection 
as to the meaning of the Howler and Harry's safety as she did.  Which 
to me suggests that she might be a bitter squib and know much more 
about the wizarding world than we have been lead to believe thus 
far.  And, back to her recognizing the sender of the howler, how many 
meetings has she had with Dumbledore over the years?