Listen to Aquakeeper. Just the fact that you are asking these questions means that you have limited knowledge about this, but are at least intelligent to ask. Here are a couple things to consider. Get your wife measured for the correct drawlength and see what she can handle VERY comfortably.

If you don't yet know what draw she should be then here it is. Measure her wingspan and divide it by 2.5 This should get you very close. Weight is going to be a personal issue.

Here's another reason to go to your local proshop. She should get a few lessons on shooting form. Grip being a very important one along with bowarm position. If she gets the right lessons she'll almost never hit her arm. If she hits her arm and gets a few strawberries you're gonna be in the same boat as the handgun. She'll quit. Let's face it. That string hurts. And don't think arm guards are the cure. They are only a coverup for bad shooting form or ill fitting equipment.

You want her to do things with you, right? Do it right. Take her where she can get the proper help.