THere's probably not much point tin adding her name to the mortgage. If you are on a tracker, interest rates are very low and chance are you are already claiming TRS for the full amount of interst.
If you are a first time buyer you can claim TRS on interest up to 10,000. So as you are on a rate of 3.25% your outstanding loan would have to be over €310,000 before a second person would start to take effect. Although the bank would probably be only too happy to add your gf's name to the moertgage (extra security for them), there would be a lot of fees associated. She would also lose her first time buyers status which could be very useful if you ever decide to move on. She could avoid stamp duty, better TRS, better bank rates ettc.