what in the...?

Just wondering what you poodle people think about this...

A friend stopped by this evening sort of unexpectedly to drop something off that he'd borrowed from my partner. He's been here once before (since we got Bennie) and while she initially barked at him then, she did eventually accept his presence and settled.

THIS time (months later) she was RELENTLESS at either barking or making quiet low rumbling. I played LAT with her, tossed some treats in her treat ball, and tried also taking her to another room. The only time she was quiet was if I was shovelling treats in her mouth continuously.

She was definitely not a happy girl. He was fine with her sniffing him and fine with leaving her be.
He is a gentle giant and we've known him for a number of years now. Definitely not a person to be wary of, from a person's perspective.

The only thing I can think of is
a) she smelled his dogs on him (weird that that would be an issue given that she tends to be fine with dogs).
b) we don't often have people here, but when we do she is fine and if anything excitable to interact.
c) she is approaching her heat cycle (?) and extra apprehensive (?)

This final piece is where I tend to lean. Her first heat was back in August right after her first birthday. It was pretty non eventful though I do remember her being a bit more alert-bark-y than usual.

Thoughts? The barking is so unnerving for me... I accept she is a dog and will practice patience. But sounds, particularly sharp loud ones, jangle me so much. I'm pretty sensitive to sensory stimuli.

IF it is an impending heat, please tell me that behaviours will come and then go again. I don't want her to lose her easy going people loving nature.

ETA What to do about this behaviour when it happens? I want to soothe her and assure her all is well, but nothing I did tonight was working.