If you add them as an additional driver you're taking a risk as a claim by them will go against your policy and affect future premiums. Don't be fooled by protected NCD - you may retain your 60% discount but it'll be 60% off an initial premium that is double the one you were quoted last year.
I'm not sure if she'd be able to insure a car that isn't registered in her name. You can sometimes add a temporary car for a short time - couple of weeks for a hire car or one you've borrowed or just bought for example. You'd also need to be confident that they'd pay the insurance and not miss a payment - if she's no insurance and it gets damaged, stolen or written off and you'll left with a potentially huge debt and possibly prosecution as it's your vehicle and you're responsible to make sure it's insured to drive on the road.
I took a loan out for a friend and she paid every month without fail. Until she was off work ill for three weeks and fell behind with everything as she didn't get paid. Luckily it wasn't a lot and it could cover it until she got back on her feet. Is there a chance your friend could end up like this? The first thing that'll go unpaid is the insurance on a car that isn't hers and that she can't afford to put petrol in.
I'm assuming you're on a lease purchase plan? Wouldn't you be better returning the car early and clearing the remaining payments.
Don't forget your insurance company may still charge you a full years premium as cancelling late into the policy can attract ridiculous fees. You'd also lose this years NCD - not a problem if you've got five or more but could be worth leaving it to run if you need to build them up.
