As previously reported on Afloat.ie, the Cork city resident had plenty of experience to fall back on when taking on the challenging 24km course around some seriously rocky and exposed coastline, setting out at 6.50am for an early start.
But she made short work of the feat, making it round the island in a blistering 7 hours 14 minutes.
Cashell was accompanied by RNLI crew members Marney T O’Donoghue, Sean Bawn O’Sullivan, Cian Murphy and Alan Cody and supported by her own team of Owen, Ray and Rob from Cork City.
The Castletownbere lifeboat Annette Hutton accompanied her for the final leg of the swim, and she was warmly welcome by her relatives, friends and RNLI supporters when she reached the finish line.
"This is a marvellous achievement and we are delighted that Carol completed the swim around Bere Island without a hitch," said local lifeboat fundraising secretary Sheila O’Driscoll.
"It is great for our local lifeboat that Carol is using her swim to raise funds for us and we are very grateful to her."
Lifeboat station mechanic Marney T O’Donoghue made a presentation to Cashell on behalf of the RNLI at a gathering in the lifeboat station.
Speaking afterwards, the swimmer thanked all who had supported her on the day and helped make her latest challenge a reality.