You will be disposing of a property so you will pay Capital Gains Tax on any gain, but will get relief for the period it was your Principal Private Residence.
The CGT will be based on the market price and not the price you sell it for.
Say it's worth €400k and you sell it to her for €400k but she pays you nothing up front.
You don't charge interest.
She repays at €1,000 per month.
The €400k will be treated as a loan and so you will be giving her a gift of around 2% or €8k a year. €6k will be the small gift exemption, and €2k will be set against her €400k Lifetime CAT threshold.
The payment to you will be the repayment of a loan so won't be taxable.
She won't get any tax relief on the repayment as it's not interest. (She probably wouldn't get tax relief anyway.)