I try to only have my players get direct “face time” with Gwendolyn at the beginning and ending of a campaign. During those scenes, I try to play her as caring for the mice of the Guard, but also knowing that for every patrol she sends out, at least one of the guardmice will not return. She is caring, but hard, and devoted to the greater good of the territories above the needs of any one specific mouse.
In the sessions where Gwendolyn is not directly interacting with the guardmice, I prepare letters from her to them. I’ve found a font that I think works well, and use it for each letter in order to maintain continuity. (I’m actually considering giving the patrol a letter from a false Gwendolyn, with the only clue being that the handwriting is different than what they’ve seen in previous letters.)
Every session at least contains a reference to Gwendolyn, even if it’s just to inform the players that they are currently operating without direct orders, or something like that.
In person, I do not have her directly addressing tenderpaws (or even referring to them by their names), preferring instead to address the senior member(s) of the patrol, thus enforcing a bit of a military feel. One of our members was a grizzled veteran, whom the group and I more or less figured that she must have had some kind of a not-so-great relationship with in the past, based solely on the tone she uses with him in her letters. In the Winter session, when (if) the patrol’s tenderpaws earn their cloaks, they’ll receive the honor of being presented to the rest of the Guard as full members, as well as actually getting a private one-on-one chat with Gwendolyn.