When Hostile Takeover steals Rek'sai after her 'When I Attack' ability has triggered but before it resolves, who controls the ability?

Ruling: When Rek'sai's 'When I Attack' ability triggers and goes on the chain, the controller of that ability is locked as whoever controlled Rek'sai at the time it triggered. If Hostile Takeover steals Rek'sai after the ability has triggered but before it resolves, the original controller (the attacker) still controls and resolves the ability.

Sequence:

• Rek'sai attacks and her 'When I Attack' ability triggers
• The ability goes on the chain with the current controller locked in
• Hostile Takeover is played in reaction, stealing Rek'sai
• When Rek'sai's ability resolves, it is still controlled by the original owner who triggered it