O' considers her frame as stationary when the train station rushes by. A' and B' photons are emitted simultaneously in her considered stationary frame just as O' is at M in the train station frame rushing by. The A' and B' photons arrive simultaneously at M. O' is considering that the photons B' and A' must reach her simultaneously as she has considered herself stationary. However, phyisics doesn't cooperate. The photons arrive simultaneously at M in the train station considered by O' to be moving as light speed is invariant under motion of the source. O', considering herself stationary will be waiting patiently for the simultaneous arrival of the B' and A' photons. When the B' photons arrives first, she becomes confused, and starts to blabber SR mantras in a vain attempt to correct what she knows to be wrong, physically wrong. The photons have to arrive at her position simultaneously because, dammit, she considered herself stationary, Doc Al told her she could do that. However, as the light speed is still invariant to O' she is still going to collide with the B' photon earlier than she detects the A' photon for the same reasons she did so when the sources were in the stationary frame, the reasons being the laws of physics makes her considerations of her stationary frame silly and I might add, impossible.
When you are moving, you have to keep up the speed or else you auger in if considering yourself stationary. This is what is known in SR theory as the SR stall speed.
Another point to broadcast is that in all these cases the realtive velocity of the observers and photons is crucial to determining and predicting the correct outcome of the events.
Hence, what is simultaneous in the moving frame is simultaneous in the stationary frame, hence a violation of the relativity of simultaneity.
And the real joker here is that what is simultaneous in the moving and stationary frames, the emission of the A' anad B' photons, will be determined by O' not to be simultaneous at her position when she detects the staggered arrival of the B' and A' photons, even if she considerd herself stationary, damn, damn, damn.
So we have a return to absolute speed, zero in this case, also absolute time, I might add.