The Washington bullpen allowed just two runs in 15⅔ innings over three games against Cincinnati.
The White House staff secretary replaces David Warrington, who is leaving for the private sector.
The Democratic congresswoman, 36, said she made the decision to undergo the fertility procedure to “feel more in control of my life.”
The left-hander, a former protégé of the departed Foster Griffin, delivered a solid performance in Washington’s 8-2 victory over Cincinnati.