I'll do my best to help out here So first of all, she would need the types that look like cigarettes, rather than the tanks you fill with liquids. They appeal to people first getting into vaping because they look and feel like a cigarette (you can even get ones where the battery lights up red on the end when you toke - most do). They also usually have an automatic battery so it turns on and off just by taking a drag then stopping. They're just generally very simplistic and easy to maintain - just need to clean the battery connection with tissue sometimes. Ideal
You can get starter kits which include everything you need. After that, you'll just need to buy replacement Cartomizers (the things that screw onto the batteries which are pre-filled with liquid and ready to go), and replace batteries when they start dying (most are guaranteed for 6 months, but you can get maybe a year out of them before they don't hold a good charge anymore). Catromizers come in different flavours and nicotine levels - you just screw them on, vape, then chuck away when they're finished (I'd normally get about 2 days out of one of them, but I vape pretty furiously lol). They're already filled for you and not designed to be refilled (though I have refilled some before! But don't worry about that part..). From what you say, I would probably start her on 12mg nicotine and see if you can get her down to 6mg, then 3mg, then 0mg maybe! Just for reference, I used to smoke about 10-15 rollies a day (not as brutal as cigarettes. I made them quite thin compared to most people too). I found I wanted 18mg nicotine to start with on Ecigs, because more nicotine gives a stronger hit, and when you're used to sucking in hot smoke.... Nowadays I'm on 6mg and I find the hit to be enough!
A starter kit will probably need to be bought online and will cost around 50 quid (high street shops usually don't have much choice with kits). It should come with a charger, a couple batteries, and about 10 cartomisers, maybe a little hard case also. She'll definitely want 2 or more batteries, btw! You need a charged one ready to go each time the other goes flat.
Cartomisers tend to come in 5 packs and cost around 8-10 quid. They vary wildly in quality and how long they last from each brand. It's a bit of minefield out there with all of this type of stuff.. Occasionaly you'll get one that's not wicking properly and will taste all crappy and burned, so if she doesn't like her first hit, try a different cartomiser incase that's what's happened They also taste like that when they start to run out/dry up and you need to replace them.
When I started out I was using a company called Green Smoke. They were probably my favourite for the cigarette style ones we're talking about here, even if the flavours were a bit too powerful for my liking: http://www.greensmoke.co.uk/
"Red Label" were my favourite. They're sort of an American style cigarette flavour, but not.. Good one for people coming straight off tobacco though!
Look around for discount codes too. I found one for 15% off on a random website and it worked
I believe they do some kind of plan where you can get stuff delivered every month without having to keep ordering. If that's not a good solution, then you're basically left at the mercy of whatever the shops in that area are selling. It has become more common for newsagents and supermarkets to sell these things now, so I'm sure you'll find something Hopefully they'll be good ones.. There are one company that I've seen in a lot of shops, and they're a right rip off. I only wish I could remember the name, because you'd want to avoid them.. Sorry :/ You should be able to recognise them by the price though if you remember how much it normally is for a pack of 5 cartomisers. They'll be charging 5-7 quid for 2 of them or something (they don't justify the price, trust me)..
Hopefully that's helpful! Let me know if you want any more advice and I'll see what I can do