I am kind of working my way to a theory that Reeva locked him out of the bedroom, he tried to break down the door, then ran and fetched spare keys when that failed. As he opened that door, I think it was her screaming 'Help' from the balcony.
Then I think she just made it to the toilet before OP got to her - maybe she even knocked him down, as he might have been off balance on his stumps, with his legs locked in the bedroom with Reeva.
At the locked toilet door, a furious OP realized there was no spare key for that one (many people wouldn't keep a spare for a door where the key is never supposed to be removed). He bashed it with the cricket bat (and the tub, in pure temper) and woke Dr Stipp up. OP was on his stumps at that time.
Perhaps there was a verbal threat to use the gun now.
Then he sighted Reeva through a sliver of a crack in the door, she began the bloodcurdling screams that woke everyone in the neighborhood, and then shot her through the door, until she stopped screaming. Bang...bang bang bang. OP was on his stumps at that time.
OP rushed to put on his prostetics.
Then OP conducted a final blow with the cricket bat (1 diff. mark on the door) and afterwards he pushed in the panels with his strong, bare hands, reached in for the key on the floor, checked Reeva was dead and obstructed her airway if she wasn't... and then began the staging. Which I haven't worked out yet and think was improvised, to say the least.