When I started letting my cats at first I did it for 10 minutes at a time, building it up gradually, and getting them to come in by shaking a box of Whiskas Temptations and calling for them, it worked well and now they go out for a couple of hours at a time and always come back home.
Dogs really scare me too (my cats' mother was killed by one but that dog has since been pts), my next door neighbour has a black labrador so I was very cautious of him but have since seen the cats in the garden with him and he doesn't bother with them.
I saw some kind of terrier and my Belle sniffing round each other the other week, I was scared and called Belle in, as soon as Belle was in the gate the dog was barking and growling through it. Belle slid out under as unconcerned as you like and the dog ran like hell
It was scared of him. Poor thing.
The road would definitely worry me too, but if she's been used to being outside before she probably have wariness over roads.