It's worth pointing out that Falkner was a bit of a non-entity when she was appointed -- basically nothing is now available on google linking her to anything trans related prior to her appointment in 2020. In late 2020 Truss with her four commissioner appointments and appointment of Falkner kicked off a major board led reform effort within the EHRC seeking:
"... radical change by re-positioning the Commission as a rigorous, objective regulator in the field of equality and human rights as opposed to its perceived historic position as an advocate for activist groups."
There was immense resistance to that amongst the staff and leadership of the EHRC which culminated in a very public investigation of Falkner herself for misconduct. A investigation against which she defended herself out of her own pocket and was completely cleared. (Of note is that the the compensation for the chair is per diem.) Over all it's been a brutalizing experience for her and her accomplishments over that adversity are very considerable.
SexMatters has an outline of some of the events and links to resources at: about us | what we are up against | ehrc timeline (no web link because previous links seem to have caused a post to become blocked)
So, Stephenson's roll will be presumably different from Falkner -- carrying on with the new mission rather than leading a major institutional reform. And she's likely to be very well briefed about what she's likely to be up against. It seems inconceivable that her capability (and willingness) to engage the issue weren't carefully considered for such a lightning rod appointment.
In addition, we owe Falkner a huge debt of gratitude. She's a pivotal figure in turning the tide against the trans insanity. It cost her a lot but she saw it through (and then some).