Open and shut constructive dismissal cases do not normally lead to such high payouts. If anything, they are pitiful. I suggest you check the formulas ETs use to calculate constructive dismissal awards.
Regardless, a confidential settlement was agreed, not an award from the ET. We do not know what the settlement was. It could be less than what was offered or it could have been more.
If it was more, then I believe that she has something against the club.
It could well have been that the £1.2m offer had expired before the ET. With the prospect of being faced with cross examination by the ET panel, she may have accepted a lower payout.