I used tena and they are quite good, also good are attends and I am about to try the abena range.
You could try adult pull ups , available from most boots and some asda branches, for some reason people find these more acceptable than full nappies.
If you think she can handle the truth then why not just tell her, it would certainly make things easier, you may want to play down the sexual angle and talk about stress relief or IBS or something along those lines.
Your only about 20 miles from us, do you know Patsy from Patsy publishing as he is up your way ?
Dave