[@NecroKnight] The letter went out as soon as Aegon was crowned, and Aemond left the same day. Let's assume he gets to Storm's End within a few days. 

We could have it that Lord Borros called all of his bannermen to Storm's End to discuss the succession, as in the thread, we specified that a few lords would try to convince Borros to support the Greens. Helia would certainly be among the bannermen called to court.

Also, Aemond and Lucerys both went to Storm's End in canon.