Lee's Modern Reloading 2nd Edition has lead 158 grain over 3.1 grains HP38 @782 feet per second as a starting load. I have used this to good effect in a Model 642 snub. It also lists W231.
Better look at that again, you have the data for HP38 mixed up with the line below it for Unique.
Lee's tends to have starting loads a bit on the "warm" side if you are looking for a real powder puff. For example the correct data for Unique with a 158 grain lead bullet is a starting point of 4.1 grains at 727 fps. Max load listed is 4.7 grains at 815 fps.
When hunting for powder puff loads IMO the best place to turn is the Lyman manual. Here there are 2 choices that can give some guidance for a powder puff. BTW, Lyman uses a Universal Receiver for testing and I don't see any notes about venting, which probably explains the higher velocities that those listed in the Lee Manual.
For a 158 grain linotype Flat Point bullet the starting point is 4.0 grains of Unique and a velocity of 791 fps. Pressure for this is listed at 13,100 CUP. Max load for the 158 grain bullet is 4.5 grains at 871 fps and 16,000 CUP. Length is set at 1.445 inch.
For a very slightly lighter 155 grain linotype Semi Wadcutter bullet the starting point is very much into powder puff territory at 3.4 grains for 601 fps at 8,900 CUP. Max listed for this bullet is 5.1 grains for 895 fps and 16,100 CUP. Length is set at 1.460 inch.
So, here we have data for 3 combinations using Unique with results that are somewhat conflicting. What it points out is that any Reloading Data we see should be considered as only a GUIDE and that we personally are responsible for developing a safe load that does what we want it to. It also illustrates that a Chronograph should be considered essential for anyone thinking about working up maximum velocity loads in any caliber.
Good news is you're looking for reduced recoil loads so the only real safety concern would be to produce a squib load. Since you are using a lead bullet it's also another plus in your favor because you won't see the wider variance between Static and Dynamic Friction exhibited by copper jacketed bullets. This means you have a bit more margin for error using loads below the listed starting point.
Personally, I'd start with a 3.4 grain load of Unique using that 1.460 inch overall length if that puts the cannelure in the right spot. Then I would take 20 rounds out and try them out while paying attention to my target and the sound for each shot. First, you want to see a hit on target each time you pull the trigger, it means you didn't squib the bullet. Second, you'll want to see nice round holes, if you start seeing keyholes you'll need to increase the velocity a bit. Third, you'll want to observe how it feels. The fact is that if bullet and barrel are a good match in terms of diameters you can work down to some really soft shooting loads before you start seeing keyholing. If you have access to a Chronograph, I would suggest working your loads to 550-600 fps velocity and see how your wife likes shooting them.
Final notes. Unique gets pretty dirty when you load it to reduced pressures. Right now you'll just have to accept that it's a price you'll have to pay for loading soft. Unique is also a rather poor metering powder so I STRONGLY suggest that you hand weigh each charge and line your casings up for a final peak at the charged casings before stuffing in the bullets. This means you don't want to even think about doing this on a progressive. If you do load on a progressive this light using Unique I can almost guarantee that you'll load a squib or near squib.