As has already been said. As long as she's insured on your car, you've got L plates on, you're over 21 and have held a full license for over 3 years then you can take her on any roads except motorways.

I helped to teach my sister to drive when my dad wasnt able to give her lessons.

One thing to note though is the car is still your responsibilty so if she gets done for speeding you get done for speeding etc. IIRC