An example of an article that claims that stall speed is reduced in a slip.
Aerodynamics of a Final Approach Slip Explained | Aviation International News
Incidentally, for a thought experiment imagine a cylindrical fuselage and a normal wing, rotated from normal flight to 45 degrees to the direction of the airflow.
The angle of attack of the wing will be reduced, but the angle of attack of the fuselage will stay the same - zero (assuming initial airflow was axial).
Now increase the angle of attack of the wings until it is the same as the original. Obviously there will be some blanking by the fuselage, and the wingspan will be effectively reduced (and chord increased). However, the angle of attack of the fuselage will now no longer be zero.
Ergo we may expect the amount of lift caused by the fuselage to increase from zero when the angle of attack was zero, to something. Assuming the amount of lift created by the wing remains constant, and given that the amount of lift contributed by the fuselage has risen from nothing to something, we can now reduce the angle of attack of the wing by a small amount until the total amount of lift (fuselage plus wings) is equal to the weight of the aircraft - i.e. the same as in the initial unslipped condition.
And putting some numbers into it, let's take a more reasonable slip of 30 degrees (still probably rather a lot).
The height of the leading edge above the trailing edge will be identical for an aircraft with a horizontal wing.
The chord will be 1.15 x greater.
Now, if your initial angle of attack was 10 degrees just before the stall, it will now be about 1.2 degrees less, so you will perhaps have to increase the angle of attack by another 1.2 degrees to compensate. You will have to increase the angle of attack of the fuselage by about the same amount to compensate for lost lift, and you will generate a little lift by doing this.
Looking at a top view of a Cessna 172 the fuselage seems to have about half the surface area of its wings, so assuming that it is equally efficaceous in producing lift per unit area (which it probably won't be - and I don't mean efficient because I'm expecting lots of drag) you might expect that it would now be producing about 6% extra lift relative to the unslipped condition.
In practice, I'm betting that the wings are likely to produce at least 6% less lift in a slip due to shadowing, turbulence caused by the fuselage so on reflection it seems unlikely to me that stall speed is lower in a slip.