Sidney had a long history of conflict with Edward de Vere , when Sidney was 15 he was matched to marry Anne Cecil a woman that de Vere would marry. The two men also clashed over Elizabeths matching with the Duke of Alencon which de Vere supported but Sidney did not. In 1579 Sidney had a ferocious argument with de Vere over the possession of a tennis court during this argument de Vere called Sidney a puppy . Sidney believed this to be a grave insult to his own parents and promptly challenged de Vere to a duel. The duel was actively pursued by Sidney and Elizabeth had to step in to prevent it. Stating that a duel could not occur between a Gentleman and an Earl.( An Earl was of much higher rank). Sidney was given two options either to apologise to de Vere or retire from court. Sidney refused to apologise and retired from court to live for a year at Wilton with his sister where he wrote his Arcadia romances . This argument gained national and international attention and Sidney was celebrated as a commonor who was unafraid to stand up to an arrogant aristocrat. Following this argument the two men championed opposing schools of literature. Sidney formed the romantic school of writers whereas de Vere became the patron of the Euphuist writing school. Both schools were highly dismissive of one another. Oxfordians state that de Vere was Shakespeare but it is very difficult to reconcile this with the demonstrable fact that Shakespeare constantly refers to and quotes from Sidney's work throughout all of his sonnets. Sidney is actually the pervasive influence on Shakespeare .Shakespeare did use the Euphuistic writing style at times but it was almost always with characters who he was lampooning. It is clear that Shakespeare admired Sidney but it is equally clear that Sidney and de Vere detested each other. If de Vere was Shakespeare he would not be making extensive quotes from an author who he personally disliked and also an author who followed an opposing literary ideation.
The first publication of the Astrophil and Stella sequence was a pirated edition that contained some of Edward de Vere's poetry, Mary Sidney would have been fully aware of her brothers dislike of de Vere and weeded these poems out in the authorised version of the book.