We must be looking at different figures. The ones I see here say that, yes, the head tube is .5 of a degree steeper which will increase the reach. It also says that the seat tube is .5 of a degree steeper which will decrease the reach. "O" on the chart is the horizontal difference between the BB and steerer, and is called "reach", but isn't the "reach" that you feel when sitting on the bike. Also, it's 4mm different...
Anyway, instead of talking in numbers and whatnot, how about we just look at these two bikes on top of each other and see exactly
where the difference is?
The CAAD10 is in blue, the Synapse is in red. You'll note that the Synapse actually has a longer
reach from the saddle to the handlebars than than the CAAD10 does, with the CAAD10's bars being slightly lower. You'll also note that the difference in shape between Shimano and Sram hoods, along with their angle on the handlebars makes a huge difference in fit. It's the reach from the saddle to the handlebars that determines how well the bike corresponds to a person's upper body, not the horizontal distance from the BB to HT.
Conclusion: These bikes are the same size and will fit the same size person, just with a more aggressive position. It may require a cm or so difference in stem length, a 5mm spacer, and some fore/aft saddle adjustment, but this bike will fit her just fine. The difference between these two bikes is less about geometry and more about frame shape/design. The CAAD10 is a crit bike, with straight, oversized aluminum tubes to make it as stiff as possible, which also makes it rather unforgiving on the road. The Synapse is an endurance bike with seatstays, chainstays, seatpost, and fork designed specifically for compliance. The CAAD10 will sit more aggressive and ride faster, but the ride will be much rougher than on the Synapse. That's the only difference that she will notice.