Obviously they shouldn't have followed her into the bathroom. Then again, of all the bad political behavior of these past 5 years, the ranks about 100th on the list.
On merit, the activists have a point. She campaigned center-left and has positioned herself center-right ever since. That is bad faith.
Sinema has made a poor political calculation dooming herself to one term. When she comes up for re-election, this plays out one of two ways. Either she gets primaried out, hopefully by someone legitimately center-left, or she doesn't, in which case the seat goes back to the GOP as democrats will not show up for her at the polls.