Hi
If it is French mobile,that has network coverage here, you should be using all those digits. Her number will remain the same, as if she is still in France. It's the same if you bring your mobile abroad, you retain the same number (003538...), and anyone calling you from the county you are in would need to dial the Irish international code.
However, you might be better to text her, as it'll cost a fortune for her to receive calls. Might make more sense for her to get an Irish network SIM card and use that in her phone
Nicola