"Who ignored SP and why?"
I might have this mixed up but was there some mention early on that her 1st approach to her line manager to raise the issue involved that person seeking advice or clarity, and possibly the EDI 'person' getting involved/feeding into whatever the trust's adopted position was? What happened, who made the decision, how that was reached etc. hasn't been clear so far from what I've heard/read, but I've not been able to keep up as much so might have missed that.
The key is absolutely how the trust dealt with her 1st raising the issue & who was involved in that process. The fact they left her dangling, with no response or advice on the concerns she raised, is a massive fail.
Obviously, employing a TRA doctor keen to expose transphobes & with a huge sense of entitlement, was another fail.