Verona Murphy sent a gushing email to Eamon Ryan praising him and wishing him the best in the Green Party leadership contest.
Despite being an ardent critic of the Greens in public, the Wexford TD told Mr Ryan she defended him after he was criticised for falling asleep during a Dáil debate.
In the leaked email, she apologised to the Green Party leader for not showing for a Dáil question she was scheduled to ask him. Ms Murphy blamed a scheduling mix up and added: "I will learn from the experience and hope to get to grips with the possibility of changes to schedules in the future."
After her apology she said she wanted to "take this opportunity to wish you the best in your leadership contest".
"For what its worth I have defended you on any commentary regarding your catnap.
"I understand that it resulted from hard work not lack of interest, and have no doubt it won't affect you with those who admire your ability as leader," she added.
Ms Murphy has publicly criticised the Green Party saying their plans to reduce carbon emissions by 7pc were "fantasy" proposals.
As President of the Irish Road Haulage Association, Ms Murphy said Mr Ryan "knows nothing about" carbon taxes.
During the same debate, she asked if he would put nappies on cows to reduce methane gases. Mr Murphy has suggested carbon emissions could be reduced by moving Dublin Port to Rosslare harbour.
Green Party minister Joe O'Brien called for Fine Gael to cut ties with Ms Murphy during the Wexford by-election last year after she made controversial comments about migrants.