OP? Bike Brands are sold in your favorite Bike Shop?
once again.. pick the bike shop first then the Bike..
"faster" is usually narrower higher pressure tires .. less than 32's .. 100+PSI.
though to make any real gain so she can keep up, go look at Tandems.
the air resistance is what slows bike riders down ,
... and faster you go the more it pushes back.