Alastor knew when to pick his battles and arguing over terminology was not one of the battles he particularly cared about winning. So, he let that point slide by the wayside.
The battle that did merit attention was the one he feared might be brewing behind her sudden quiet and determination. This was not the Marlene that flirted and blew kisses. This was the Auror that lived underneath that flirt -- a real Auror, not one of these half-formed ones from this generation. This was not the woman you trifled with.
"Marlene," not even Marly-girl for this conversation. Putting his hands on her shoulders, he cocked his head and looked her in the eye. "Exactly how do you intend to 'take care' of this?"