Rag, from your link,
"On the 26th of April, positioned on the Liffey, she raised her 12 pound artillery guns over the Loop Line railway bridge and fired at her first target Liberty Hall, the Head Quarters of Citizen Army. Her shots were less than accurate and her shells destroyed much of the surrounding buildings and beyond. She also targeted the GPO and Bolland Mills which Eamon De Valera had occupied."

Has anyone but Ann Robinson(?) suggested that Helga fired at GPO?
She provides a pictire of Liberty Hall after the rising which shows it holed by shells but not burned, and surrounding buildings damaged but not "destroyed" as she claims in the text.
So not very reliable.

Here again is the essay by a curator of the National Museum of Ireland, published in the leading journal of Irish History.

"Subsequently the Helga II gained an undeserved reputation for playing an essential part in the Rising. (Most of the damage to Dublin's city centre was caused by fire, particularly at premises like the Irish Times warehouse and Hoyte's Druggists and Oil Works, rather than by shelling.)"
"On 25 April 1916 the Helga sailed from Dún Laoghaire to shell Boland's mill, and on the following day fired over the loop line railway bridge at Liberty Hall. In total the Helga fired only 40 rounds during the Rising, and it is difficult to assess the effectiveness of the fire from her guns."
http://www.historyireland.com/20th-century-contemporary-history/tss-helga-ii/