Pogonina vs Chess.com Move 26. ...
26.Qb3 was Natalia's choice. I would rate that second after 26.Rb4 but it is a good move and perhaps more flexible than the rook move. The queen is still nanny for Ra4 but now looks at b7 aswell as f7. The move also takes control of the square c4, which may be an important waypoint for the white troops, especially the bishop. What are Black's choices?
26. ... Rc6 27.Rb4 Rb8 28.Be2 Bd8 29.Qa4 (xa6)[29.Qd5 (xe5) Be7 (Qxe5 dxe5 Rxd7 Bxb4) 30.Bc4 Qe8 31.Ra1 (The pawn needs a guard. I would like to play Rd3 here but Rc5 puts a stop to it and regrouping with for instance Qd3 exposes the a-pawn for Rc5/Dd8.)] 29. ... Rbc8 30.Ra1!? (d5 doesn't work Bg4!! Qxg4 exd5) Black's forces are somewhat ice-bound and it's hard to make any way.
26. ... Rc5 27.Rb4 (I think the trade of Black's pawn b7 versus White's pawn a5 is in White's favour. 27. ...Rxa5 28.Rxb7 Rb5 29.Qxb5 Qxb5 30.Rxb5 axb5 31.Rxd6 + ) 27. ... Rb8 28.Rb6 (Threat:Bd8) Rc6 29.Be2 Rxb6 30.Qxb6 Rd8 31.Bc4 and now if Bd5 the rook can go Rd1-d3 and prepare b4. The White king might need some securing measures.
26. ... Rd8 27.Rb4 Going for b6. 27. ... Be7 28.Be2 looking to doubly attack f7 and b7. 28. ... Qc8 Counter attacking Rb4, if Bc4, then d5. 29.Ra4 Qd7 30.Bc4 and continuing to build pressure on Black's weak spots.
26. ... Rb8 27.Be2 (Threat:Bxa6) Rc6 28.Rb4 Bd8 29.Qd5 (Threat:Qxe5)(29.Qa4 (Threat:Bxa6) Rbc8) and the Black Queen must move. Some interesting pressure play here. White is expanding her area of influence, so besides keeping Black busy on the queen wing something is slowly building up against the king side. Just think Bc4 and Rd1-d3-f3.
26. ...Kh8 with the idea f5 - not really
26. ... g6 might actually be a more attractive move, since all rook moves enter Black into inferior lines, altough not in any way lost. It gives some air to the king and after, for instance Kg7, the f7- pawn can move away from the line of fire. g6 also prepares f5. Loosening up the king's position is, as always, double edged, so defending f7 for a while is probably preferable.
Bg5 has a lot of options. It can go to e7, defending d6. It can go behind the lines to c1 and attack b2. It can move d8 to put pressure on a5. A line originally from ivan_the_trouble, I think. So it might be wise to hold it back for a while.
The pawn structure on the queen side can transform into different patterns. One I think is good for White is if the white a-pawn is exchanged for the black b-pawn. So it might be a goal for White.
I would say this position is a good example of how deep chess can be. It's really hard to say something for sure because the consequenses of one move stretches very, very far. Natalia is very Russian School, seeking space and pressure and if this had been a game under normal tournament/match conditions I believe Black would have cracked sooner or later. Black can still play on because the drawing line is not crossed yet, but it all has to be reasonably precise. I'm not sure that 26. ... Rb8 is the best, especially if it rests on a "must do move". If the position boils down to the opposite coloured bishop one that has been flashing here and there, there are good drawing chances for Black. That depends though on the kings' activity and the block possibilities of the white pawns. Given that, keeping at least one more piece in play would be a goal for White and that choice is totally depending on player will, which is hard to foresee. On the other side, a stubborn defence might be as trying for the first player as being under pressure for a long time.