It depends whether it's a 12 or a 30-valver. IIRC, the switch to 30-valves was during 1997, so a R-plate could possibly be either. The 12-valve had 170bhp, the 30-valve 193bhp.
I had a 99 on a T 2.8 Quattro Tiptronic, which replaced a 1.8 (non-turbo), so that sounds like your Mum would be making the same change. My 30-valver was pretty fast, but not monstrously so. You're probably looking at mid-seven to 8 seconds for 0-60, depending on whether it's manual or Tiptronic. The engine does need to be revved to get the best out of it, but it's very smooth, and has a very fluent feel to it. Keep in mind that it's a fast cruiser rather than a sports saloon, and you won't be disappointed.
Coming from a 1.8, it'll feel very nice indeed. Watch out for the fuel bills, though. These things need their own oil well.