She'd never get to use it on the MC, Tinkerer won't include that.
Sooooo...she's still a dominatrix, just not into that, but Mr. Miller has a fantasy about it and she wants to gift him one. EVERYONE will know if she gets one herself, ruining the surprise, so she asks the MC to help. I think the MC should go to Edgar first, but he doesn't have any in stock. The MC can order one (arrives in a week) or have Marcus make one (ready the next day, costs more).
As a thank you she gives the MC some pointers on how domination/submission
really works...choose whether the MC is the dom/sub. One time only, with the possibility of future help & thank yous if the MC is a good student. (Choosing dom then ignoring the safeword should have VERY serious consequences.)