I think Morgan played well enough to earn a roster spot next year, although unless you're a starter, you can't take your roster spot for granted. You never know what goes on in the minds of these GMs. Every year there are draft picks, undrafted players, free agents that are on a "camp" contract trying to take your spot.
Perhaps she was informed by the club that her contract will not be renewed, or as suggested, she's simply saying goodbye to THIS team ("this team will always hold a special place in my heart") because there will be new players on the roster next year, and maybe a player or two that she was close to won't return. They came very very close to winning the championship.