When my dear daughter passed her driving test I had the same worry. The first time she actually got to drive by herself it had started snowing before she left to come home. She did not get her license until about two weeks before her 17th birthday because her Dad and I told her she had a choice between driving or taking horseback riding lessons. She took the lessons and on top of being very mature already, the extra year helped with maturity behind the wheel. Go destress and then have a talk with her. I told my daughter that if she ever needed to have somebody come get her because she should not be driving, call and there would be no questions asked. I would rather pick her up from a party at 2 in the morning than go to a funeral at 2 in the afternoon.
She is now a 21 Univeristy graduate and has never had an accident. (I on the other hand do not deal with the snow all that well and she had to come get me once)