T.J.
I taught my gal Lisa how to shoot several years ago and she had the same problem. What she found was that in trying to keep it from slapping her arm, the string would catch across her...uh, chest shall we say.
Lisa finally found her form and has no problem with either now. One of the better break throughs she had was not to heel the bow too much. She makes sure when she grips the bow (she shoots a 1968 Red Wing Hunter with a medium recurve style grip, things are different with longbows though) that the last knuckle of her bow hand is right under the arrow.
Lisa is a right hand shooter, and discovered that if that knuckle drifts to the right side of the arrow, her elbow "bent" in and would get whacked (I called this strong negative reinforcement, she called me other names...).
As others suggested, the bow might be a little heavy. Just for now though. As your wife gets her form nailed down, it will be easier for her to shoot.
Lisa also discovered what guys have mentioned above, that canting the bow to the right (for a right hand shooter) helps with the...chest thing. This tucks the drawn bow string sort of into the left arm pit (again, for right hander) away from... sensitive areas.
A little advice if you don't mind about teaching women you care about how to do new things. I have been with the same hard-headed German gal now for 16 years. I taught her how to fly-fish (our first date actually) and how to shoot stick bows. She taught me how to make sauerbraten and spatzel. Let them learn on their own.
Resist the urge to correct every little thing. Tell them how to do it, show them how to do it. Then leave them alone. Try not to make them feel like they are doing everything wrong. Make sure that they know that if they need/want help you are there, but otherwise they can figure it out just like us guys did.
Congratulations on the recent wedding and God bless. Oh... and hold on tight, you are in for a crazy and wonderful ride my friend!
OkKeith