Yeah, he doesn't seem to be hugging a groupie. She isn't groupie-like, anyway, y'know? She's wearing a big corduroy jacket, not, like, y'know, stupid groupie crap.
And from a girl's perspective... if Mr. Plant were feeling affectionate enough to draw your face towards his (with those murderer gloves!,) would you really be pouting and giving him a sorta sideways-hug? That's not a groupie hug. Or it's a groupie in an un-groupie-mood.
Plus, most of the pics I've ever seen of Mr. Plant being ornery with groupies usually show him smiling like he ate the canary. 'Cept for that one at Rodney's English Disco, in which case he looks mad.
To continue speculating... could he hunker like that after his car accident? That'd put pressure on your ankle for sure.
I'll go ahead and blurt out the absurd thing I was thinking, even though I'm 99% sure I'm wrong and have nothing to back this with. Maybe it's his sister. Never seen a pic of her. I think she's quite a few years younger than him, and that sorta looks right in the pic. (He's 28-ish or something, and she looks sorta college-aged.) And I kinda see a resemblance... But I dunno. My brother would never hug me like that.
I was gonna google around and see if I could find a pic of her, but I didn't do a very good job because I felt bad searching for her. It seems too nosy.
EDIT: Oh! And to help with dating the pic, we gotta remember that phase Mr. Plant went through when he had the bangs in 1976. So this is before or after both his car accident and his bangs period.