I'm going to approach this a bit different and hopefully you won't be too mad.
Are you crazy, inexperienced, desperate for work, stupid?
When a customer makes a demand like that its time to call them back a couple days later, be polite and decline the job for whatever plausible nice sounding lie you want to vomit out.
I've done that job more times than I can remember. Maybe I'm the moron but realistically its not possible to brush down a brick wall without some amount of dust. Not going to happen.
You can't really wet it down because the dust and chips will end up goo.
I've tried using a sander with and without DC and that's more of a hassle than its worth.
I've also used a drill or grinder with a wire brush; that really sucked in terms of dust all over the place but it did make the work pretty fast. I would see the RAS as a great option but I doubt DC will be sufficient
Sandblasting also works well but that has limited use in a home; when a place is vacant its the way to go.
After all else I prefer just a couple of plain old wire brushes and grunts. Not the most sophisticated modern method but it works well. Sometimes its not worth reinventing the wheel.
If this is an occupied space and she doesn't want here stuff moved. Run Forest Run.
If she will allow you to clear out the room, seal it off, cover the floors and vents and put fans in the windows you've got a chance.
Realistically a client like that is going to complain no matter what you do so let some newbie fool contractor die on the job instead.
