Henry VIII?
WHo the Hell beheads an old lady?
http://en.wikipedia.org/wiki/Margaret_Pole,_Countess_of_Salisbury
Yeah, but she was royalty.
Royalty are going to get beheaded from time to time regardless of sex and age.
Septa Mordane was just a priestess of the Seven and a nice old lady.
But the answer as to who would behead her or other like her is King Joffrey :O