The womens and junior bar are exactly the same between the collars. exactly. The difference is the length of the sleeve, and also the thickness of the tubing on the sleeves, both reduced to get from 10kg down to 15kg. We have tested both up to a 400lb clean and jerk, and have no reason to believe they wouldnt handle more, or for that matter 700 or 800lb squats and deadlifts, although i have no idea why anyone would ever want to do those kind of lifts on a womens weightlifting bar or a junior bar.
If your wife is going to be using more than 60-70kg, you should go ahead and get the womens bar, just because you dont want the pain in the rear end that would come from not having room to load weights.
I know the womens bar is more expensive, but ill tell you what... I have a couple of womens bar shafts that are uncoated (still straight steel insted of black oxide)... if a lack of $$ is what is keeping you from getting a bar for the wife, give me a call and I will make you a very, very good deal on a bar with an uncoated shaft. I just have them left over from when I used to sell the bars in uncoated steel, and need to do something with them.
Once the wife does some lifts on a bar with a 25mm diameter shaft, and finds out how much better that smaller diameter feels for a womans smaller hands, believe me, she will love it.