Probably because Penny Johnson is the doctor, Claire. Halston Sage is Allara.
http://www.egotasticfuntime.com/new...e-orville-jessica-szohr-replaces-halston-sage
Egotastic, which is a gossip rag, so heavy grain of salt, but it actually has pictures this time, shows another actress who looks very similar to Halston Sage filling in for her and wearing the same uniform with the same hair color.
They speculate that that means Sage is being permanently replaced as the security chief because she's off filming her Netflix movie, but I think they might just be bringing in a lookalike to fill in for her while she's gone, and then she'll eventually come back to the role, since no announcement about her leaving the show has been made, and she's dating MacFarlane, so I'm sure he'd keep her job secure while she's gone.
So I think the new actress is just going to play Allara and no one in-universe will say anything about it, or alternatively, they can go the Becky from
Roseanne route and joke about how there's something different about her, but they can't quite place it. Or she might be playing Allara's sister or something, but she's too close in appearance to be playing someone completely unrelated to Allara, I think.
On another note, that's the Oviatt Library at Cal State Northridge they're filming at, previously seen as part of Starfleet Academy in ST09.