Stedxxx -- It would certainly be cheaper to put her on your insurance if they will have her, I don't have a clue how much more ? they will ask how long she has held a full licence for when you apply.
It's a very powerful car though for a new driver, and really think it safer and cheaper to let her get some experience in a less powerful car first, but it's down to yourselves.
Yes, if she has an accident in the Audi on your insurance, it will affect your NCD by the amount stated in the policy, unless you have it protected.
Might add, you can get a discount with a lot of insurers covering a second lower powered car yourself, with your wife a named driver on the policy, it's cheaper when they are your spouse.