Good for you on getting your wife a nice toy. I'm a little curious as to how you bought a vehicle without investigating whether it had ABS or not, though. Or investigating it's handling characteristics in the conditions you are going to operate it in. TJ's aren't known for their exemplary, sports car like handling characteristics. Oh well, that's now water under the bridge, right?
Since you are currently sliding the tires on wet pavement with the stock brake setup, locking the brakes up, the only solution is a stickier street tire and modifying her driving behavior. The best braking you will ever see is a stock sized winter rated street tire. Be aware that it will still hydroplane under the right circumstances. Any vehicle will, ABS or not. It's unfortunate that your wife is now scared of the TJ, they are fun toys. They are not a Volvo though. Good luck in addressing this issue. You may find that this issue is inherent to the design though, and may want to contemplate replacing it with a different sporty toy for your wife.
As a side note, my spousal unit drives a 2012 JKU on 33's and does just fine, on and off road. It's been known to rain on the wet side of the PNW once in awhile.