I have to say this because the lady friend will not know this.

Copper plugs are made for cars trying to make power. The car truely wants to have Iridium delco plugs in it.

I don't think she wants to change her spark plugs every 15,000 miles. Delco plugs will last 75-100k easy and are best suited for the car.

The price of you doing the job may go up, but you need to let her know that they won't have to be touched again for most likely the rest of the life of the car.