Hyawatha; My husband says I am well indowed in the chest department. I had to teach myself how to shoot with proper form with just a few ajustments made for chest clearance. First of all I never have had any problem with arm slap and I dont wear a arm protector except during hunting season when Im wearing a bulky sleeved arm coat, I did spend weeks in the hospital and undergo surgery to have pins placed in my elbow when I compound fractured it when I was younger and this may explain why I never have arm slap on my bow arm, who knows, the elbow never did heal in quite the way it was before its almost like being double jointed at the elbow.
I have never worn the chest protectors so I cant say anything about them either way.
I shoot a Parker Ultra Lite 31, which is a short axle to axle bow which I believe is a plus , a longer axle to axle would mean more string has to go farther down at a longer with less % of angle to reach the cam. the longer diatance could possibly bring the string over and in contact with the breast. The short axle to axle bow has a steeper % of angle on the string. When I shoot I have the bow at full draw and the string travels up from the cam and comes in front of the breast ( the arm pit area)but not actually touching the breast, if the string is held at full draw on the breast or inbetween the breasts she may always have a problem.I also keep my bow arm elbow bent when shooting. Make sure she has the proper draw length, to long of a draw will bring the string over the breast and cause breast contact problems.
Most shorter axle to axle bows at full draw will give you a string angle like this >.
Most longer axle to axle bows at full draw will give you a string angle like this ).
At the target I stand facing 3:00 oclock , My target is at 12:00 oclock, at the WAIST I turn my upper torsoe slightly so my left breast is facing 2:00 to 2:30 oclock , this aids me in keeping the left breast out of the way of the string.I stand up straight with the shoulders back and a slight arch in my spine at the lower back, Works for me. If she has the chance to I would suggest watching other lady archers with the larger chests shoot and pay close attention to their form, I always learn alot from watching others. Hope this helps her