Try this diagram which shows the succession plan when someones dies without a will (intestate).
[broken link removed]
As the grand-niece you are far behind the nieces and nephews.
The diagram is courtesy of
http://www.traceysolicitors.ie/faqs.html which also includes some additional help on wills.
This next suggestion is a extremely "long shot" and is not based on any experience.
It might be worth at least asking an experienced Probate Solicitor if section 98 could be applied in this case where your aunt has no children.