My wife asked me to look into buying digital drum kit for herself but I literally have no clue about those. Are they any good, what type would you recommend?
There are some drum kits at gear4music and price varies between £200-£500 so if you own any and would be able to shed some light on which ones to look at that would be hugely appreciated! 
I would say, depending on your budget either of these:
And
Both are top names for electronic drums and both would be good for learning with; if you could stretch to the Roland set it is more advanced.
We have a Yamaha DD-75 at home which I really like. We got it for our eldest but I think I play it more often than he does lately. Portable, sounds good, lots of features, and quick to put away since you can mount it to a standard collapsible snare stand.
Easily fits into your budget with lots of money to spare for upgraded pedals (we have a Yamaha KU100 for the bass drum), a nice throne and some other goodies.