Is this just a one-off show or are they pro-shooting this for a theater release? I'm not sure what the Hollywood Bowl is. A one-off show is a who-gives-a-fuck. A pro-shot version of Jesus Christ Superstar would be strange, that wouldn't make any money even if it was casted "perfectly". Better pick a more popular musical. Unless they are doing this intentionally to be controversial, which would be very 1992 of them.
Edit: This is just for 3 shows, this is "who-gives-a-shit" territory. She was probably the best and most popular musical theater actress they could land for this, especially because she will give it buzz for Wicked.
It does seem a strange choice, she must be fielding all sorts of lucrative offers at the moment given the popularity of Wicked.
I wonder if it's literally that she's got passion (of the Christ) for doing some onstage theatre, there's a window in her schedule, it represents a smaller time commitment than another movie. (I don't know how much rehearsal time it might need but Google thinks about a month) and this will be a bit of a spectacle that'll give her reason to be spoken about away from Wicked which has a sequel releasing a couple of months later.
Limited run, big star, novelty of a stage play at the Bowl.
Take into account that theatre tickets are quite expensive, if they can get people to pay $200 a seat at the 17500 capacity Bowl, (and if they allocate seating/sections somehow they'll be able to charge more for the good seats) then they'll bring in $10.5M if they sell out.
Google thinks Erivo got a million for Wicked. She could easily walk away with more for a month's work here.
Seems like a pretty good idea in that context.