Higher nicotine levels do provide enhanced 'throat hit', so it is very likely the liquid might be too strong for her. Also, most folks use their e-cigs more often than tobacco cigarettes. Vaping too much in a short period of time can also cause throat irritation.
The liquid she has can be diluted with vegetable glycerine available at pharmacies and other stores. Dilution will reduce the flavor, but will also reduce the nicotine.
"At some point you have to ask when this place changes from a vapers forum with drama to a drama forum with vapers." - Gatsby