A goal from Georgia Wilson gave Bournemouth the halftime lead, before Jenna Markham added a second nine minutes from time to send Helen Bleazard’s team into the final, where they will meet Plymouth.
Defender Harris started and played much of the game before she was replaced with four minutes to play.
Reflecting on the game, she told the Daily Echo: “It was a great match.
“West Brom were a really strong team. We knew a bit about them because we played them in pre-season, but we didn't want to underestimate them or make any preconceptions because a lot can change from August to February.
“But it was a great performance from us.
“I think we dug deep. They're a very physical team and the game was very transitional, which is potentially something that we're not used to. Usually we're quite dominant in possession.
“But that being said, I think that's the thing that is making our team so successful this year is our ability to adapt to whatever the other team are giving us.
“So nice to score two goals, and as a defender, it's always really reassuring to keep a clean sheet as well.”