He wants to level the rig first, then deploy the slide-out. She wants to level after the slide is out, because it seems like the rig "leans" a little bit after the slide goes out. What's the answer?
Courtesy US Patent Office
The safest (and most warranty-wise) answer: Do what your rig's manual tells you to do. Here's a lift from a Keystone manual: "The recreational vehicle must be level to avoid binding the slide-rooms. Remember, stabilizing jacks are not capable of supporting the weight of you vehicle! They are intended only to stabilize the unit maintaining a level condition. Non-leveled conditions cause sticking situations providing damaging strains on the slide-out mechanism."
This advice is pretty much standard among the majority of the RVing crowd. If the rig is twisted, even a bit, it can put a real cramp on the slide-out mechanism. Pinching your slide-out can make for a most uncomfortable situation--particularly if you can't 'reel the unit back in' when it's time to hit the road.
As to the case of the 'leaning RV,' we can only say: If your rig leans after you deploy the slide-out, the most likely issue was not having your unit properly settled in the first place. Were the levelers on firm ground, or did they perhaps "sink" a bit into soft ground? Here's a case for leveler or "jack boots" that give a larger surface area to those little feet.