The fan was conscious as she was carried out and taken to a local hospital, according to the Cubs. Medical personnel placed her head and neck in a restraint.
The fan was sitting a few rows from the field in a section just past the first-base dugout and camera well, where seats were added several years ago.
The liner by Cubs rookie Kyle Schwarber appeared to strike the fan flush. First-base coach Brandon Hyde, positioned nearby, immediately reacted by putting his hands on his helmet.
"Awful, just awful," Cubs manager Joe Maddon said of the incident following the Cubs' 9-3 victory.
Sunday's game was delayed briefly as fans and ushers waved for medical personnel. The game resumed shortly as medics treated the fan and applied ice to the affected area.
An inning later, a fan sitting behind the third-base dugout was struck by a bat thrown by Chicago's Addison Russell on a swing. That fan was treated briefly and remained in the seating area.
There have been other incidents of fans being injured by balls or bats flying into the stand at ballparks this season.
On Friday, a female fan in Detroit was injured by a foul ball behind theTigersdugout.
Earlier this year, a Massachusetts woman was seriously injured after being struck in the head by a broken bat in the stands at Fenway Park.
Last month, an Oakland Athletics season-ticket holder asked a federal court in a lawsuit to order Major League Baseball to extend the safety netting at its ballparks the entire length of the foul lines.
Maddon was asked what can be done to improve fan safety.
"Pay attention," he said. "I hate to say it, but ... those are wonderful seats. You probably pay a lot of money for them. You're digging the fact that you're right there. I watch and you see people turning their back to the field when the action's going on. You just can't do it."
When asked if extending the screen behind home plate was the answer, Maddon said, "I don't know how that plays. I don't know what that means. That would be a [question] for someone other than me. But what I'm saying is, when you're at the ballpark and you're in those particular locations, watch what's going on. Don't turn your head away from the action. Every time a ball is pitched, you look, you look and see, and then you can go ahead and talk.
"That's probably the best answer, honestly, just to pay attention. I know when my family's there I absolutely insist that you watch what's going on."
Fan safety at MLB games
The Baseball Tonight crew discusses fan safety at MLB games after multiple spectators have been injured this season.