Mick,
One resort I would recommend for what you are after is La Thuile in the Aosta valley.
If you stay at the Planibel (either in the hotel or the self catering apartments), then it is a two minute walk to the lifts. From there it is a gondola up to mid-mountain, and for your girlfriend there is then a chair which takes you two a number of quite long greens which are very gentle, and also very wide runs, which should help her. It does not get particularly crowded either, so that should help her confidence.
In the same area there are a number of gentle blue runs, which are also very wide, so that will give her something to progress to once she has hopefully mastered the easier runs. The runs are north-facing as well, which will help in April.
I recommend a private lesson from one of the instructors there, that way they will only be push her as far as they are confident she can manage, and when I used one on my first skiing holiday it really helped me realise my potential.
There are quite a few reds and blacks to keep you happy as well, so it could be a good place for the pair of you. Not the liveliest of villages, but a few decent restaurants, and the Bricole is quite an enjoyable bar which we have spent many a happy hour in on our trips there.
Good luck.