My own thoughts:

Your wife could get a much lighter weight hybrid bike with normal sized wheels and much lighter tires, and it doesn't have to cost a fortune. there are many great tires out there that are fairly thin (25mm) and have Kevlar inner belts that can take her safely over even the roughest gravel. Lighter/larger circumference wheels and lighter tires can make a big difference in total bike weight and being able to keep up with others.
The gearing on such a hybrid would likely be easier too for all types of hills than the heavy bike she has now.

Try weighing her bike, then bringing her bike with you to a good bike store and asking to see lighter weight hybrids with wider range gearing and normal sized wheels and tires. And they should be happy to put whatever tires you want on a bike you purchase- likely for free.
A typical hybrid with straight handlebars and handle grip shifters would be way easier and reassuring for her than trying to jump right into roadie drop bars.

P.S. I love love love my helmets mirrors, and I wear progressive tri-focal glasses and fit-over sunglasses too.