I agree that two (or more bodies is the way to go if you can afford it. Also, changing lenses quickly like that is just an accident waiting to happen. Her luck will run out eventually and that will be a costly mistake. Also, as you say, dust on the sensor at wide apertures isn't much of an issue, but dust on the lens will spoil the bokeh pretty quickly if there's enough of it and it's big enough. Not that most people would notice...One thing telling, an excellent portrait/wedding photographer in our area, can easily afford any gear. She uses the ef 50mm 1.4 for some fill-in shots of guests and details at weddings. I asked her why she didn't go with the L version as she did with every other lens (including the 85mm), and she said she had tried it and decided it just wasn't reliable enough for what she was doing with a 50mm.
She mainly uses the 24-70mm f/2.8 II, the 85mm f/1.2,II and the 70-200mm /f2.8 IS II. And you should see how she holds a lens between her knees when swapping out! Changes lenses faster than anybody I've ever seen.
I wonder how often she has her sensor cleaned. Admittedly wide aperture images (shot indoors with darker backgrounds) don't show dust spots very easily, which is probably why she's not very cautious about changing lenses so much. But I wouldn't want to buy anything she sells used, after she's done with it. You can't change lenses "fast" without putting excessive wear on the mounts. It's far better to just use more than one camera body, so you can leave lenses in place and switch between them. She should do this, especially since you say she can afford to purchase whatever she needs.
Changing lenses too quickly is asking for trouble - having two bodies helps.
At the week end I shot a wedding with 1Dx + 70-200 and 24-70 on 5DIII - which was great until I wanted to swap the 70-200 for the 85L. Even in the heat of the moment, it's worth taking a few extra seconds to change lenses especially the rear element of the 85L so far out! It would be so easy to damage it.