Monahan is a daughter of PV Doyle and one of the beneficiaries of the sale of various Jurys Doyle assets in 2006. She is a shareholder in the Doyle Hotel Group, which owns the Westbury Hotel. Along with husband Ray, Sligo-based Monahan and her family invested heavily in property at the top of the market.
In 2015 their vehicle Sandlake Properties bought back some of son Neil's borrowing from Ulster Bank at an 82pc discount. The family's Monti Property had 300m in assets spread from Cabinteely to Poznan. The Monahans also own the Terra Monti vineyard in Languedoc as well as Sligo's popular pub Hargadon Bros.