Same thing happened here. After visiting/staying in Munich, Salzburg, Venice, Verona, Florence ... she wants to return to Lake Bled at least one more time. Other ones she can take it or leave it.
OP, make sure you follow the road as shown in the map:
Get off the highway around Villach and don't go back on a highway until you get to close to Jesenice. Stop on the road shown in the map between Kranjska Gora and the highway entrance on one of the obvious places (there will be picnic tables or simply a parking spot). River is just 30 ft to your right, walk down to the river. After a night in Bled ask your wife if she wants to go back to Austria or stay. Worst case scenario, Austria is only 20-30 minutes away if you hit a highway at first opportunity.
If she wants to stay, ask hotel staff to show you how to get to drive the road all locals call "Dolina Soce" (last time I did it was 20 years ago and I can't really remember how to get to the right point to start driving south). As long as you keep the brakes reasonably cool, you both should hugely enjoy it. After that, at Nova Gorica, you can go back to highway towards Ljubljana and continue on your planned route.
Another very famous spot is Postojna and a cavern tour. If you have been already to Carlsbad, NM then this is about the same, only this one is "alive" - meaning, water is still dripping profusely and formations are still in process of growing throughout the cavern.
Hope you will have a lot of fun regardless (Slovenija OR Austria).
EDIT: the hotel to stay in Bled is Hotel Park, but ONLY if they guarantee you lake view room with balcony. Make sure you get that. Below two pictures from our balcony taken by my wife with point-and-shoot. Horrible quality, but it will give you an idea.