She took the seat vacated by Jim van der Poel in the annual election for three directors.
The other two re-elected this year were sitting directors John Monaghan, Wairarapa, and David MacLeod, Taranaki.
The unsuccessful candidates were Gray Baldwin, Putaruru; Grant Rowan, Southland; and Garry Reymer, Cambridge.
The Fonterra Shareholders’ Council in the election results announcement said that Guiney lived and farmed near Fairlie where she was a director of four dairy farming companies.
She had previous experience as a consulting officer and dairy production lecturer and had studied overseas co-operatives in the Netherlands and Ireland.
With husband Kieran she was the 2014 winner of the low-input Dairy Business of the Year.
Along with others Guiney opposed the introduction of Trading Among Farmers in 2012, calling it a flawed concept.
