Howdy, playtester here to say that the process you listed for Vivienne's rapture grind can be sped up by having the Hero stance swap instead of using an ability since it is mechanically faster to hit the swap stance button and select a different stance, the stance menu can be opened while abilities are resolving so you only have to one click and no mouse movement when your turn comes, and also stance swapping has no ability card that pops up when used so it saves about a second each time you do it just based off that alone. Also, if you really want to grind out her rapture it is best to wait until you've gotten past the Withering Grove as there are some bonuses to Rapture gains you can utilize after that. I have personally passed several ideas to the dev on how to give Vivienne more Rapture sources but if, how, and when those get implemented is ultimately up to CM.
Also, Vivienne not being able to use weapons is an intended mechanic. In fact, any lingering mentions in-game of Vivienne having weapons, a helmet, or a shield for in moments of environmental interaction like in the smith's shop are considered bugs and if any are spotted it would be a great help to report them.