Mrs Gallagher (36) is now expected to add Shannon name to any legal proceedings.
Shannon (15) was found dead last week, less than two months after Erin (13) died amid claims she had been bullied.
Mrs Gallagher said she is angry and numb at the deaths.
She said she has no doubt that Erin's suicide directly led to Shannon's death -- her eldest daughter's personality completely changed when Erin died.
Solicitor Patsy Gallagher said his office has still not received a reply to the letter sent to Donegal VEC. He intends to take proceedings against the HSE.