Since I was one of the ones asking for people to explain -1 votes in this thread, I thought it is only fair for me to chime in here with what reservations I have about this.
On the one hand, I am a bit of a “commit bit maximalist” since I don’t think there is much if any downside to giving people commit bits prematurely. There was apparently a stretch of time in the past where attending a sprint was enough to get a commit bit, and as far as I can tell there were no real ill-effects from this.
On the other hand, if I were judging “readiness”, I am not sure I would have enough information to go on here. It seems to me that a big part of being a core dev is reviewing PRs and making decisions in issues - one could make the argument that you mostly only need the commit bit in order to do reviews, since hopefully even core devs are getting reviews before merging. It seems that she has done very little in the way of reviews, see this query, which turns up 6 closed and 2 open PRs. Most of these are procedural comments and two useful reviews of the wording in documentation 1, 2.
From speaking to Joannah and discussing issues with her, I will say that she is smart, capable and responds very well to feedback (and by this I do not mean that she capitulates - she formulates well-reasoned responses that sometimes agree and sometimes disagree with you). I would have no problem voting +1 based on her potential - I think that even if this vote fails, it will definitely happen eventually and I don’t see a particularly significant risk here. If I were voting based on whether I think she needs a commit bit right now, I would probably vote -1, unfortunately.
For now I will abstain from voting, and I hope that my comments here are taken as the constructive feedback I intend them to be, and not as a criticism of anything innate in Joannah.