This allows Black to carry out precisely the plan I outlined in my previous comment - the move order being changed, of course. I like 41.Qe2 myself, but reckon 41.Qb7 is the more flexible, combining defence with counter-attack.

I actually thought this move might still save White...

I don't think there is any real prospect of this counter-attack succeeding. Probably passive defence is called for: 45.Qe2, but after 45...g5 46.fxg5 Qxg5ch Black gets her passed pawn. But it's a rook's pawn - notoriously hard to make good in the late end game. Black would still have plenty to do to bring home the win.

I considered only 46.Qe5 myself. It is hard to see that 46...Qd2ch achieves very much. If we have to assign a losing move, this would have to be it.

Here's an amusing line: 49.Kg3 f4ch 50.Kh3 Qf2 51.Qe5ch g5 52.Qe8#! Of course Black doesn't have to be so careless: 50...Qd5 looks good enough.

White's game has become almost impossibly difficult. The sort of line the PMCA gives would be very difficult to imagine, I think. Probably the clincher for me is that this move really places the Queen in a straitjacket. After Black's next move, Black is caught in a 'zugzwang'. Seeing that would have forced me to look abroad for some better defence.

Zugzwang. White could have resigned right here without raising any eyebrows.