It is the day before Sisterly, a women’s health and wellness company, celebrates its third birthday in late October. Three years in the business and Sisterly has now sold over 1.5 million sachets of doctor-formulated women’s health supplements.  The business, which was co-founded by three friends called Louise O’Riordan, Jennifer O’Connell, and Aoife Matthews, is planning to mark the occasion with a gathering of 100 customers in the five-star Merrion Hotel, before a walk around the nearby Georgian square. I am meeting O’Riordan, a luxury brand consultant who lives in Los Angeles, and O’Connell, a former barrister who has completed two…