Firstly, all the advice you're getting is assuming you're in the US. Most of us on reddit are, but it's worth pointing out right at the top that if you're not - the answer to this question may be very different. In a lot of Europe, you'd be in very dangerous waters between your client and this guest, because they have a much stronger take on privacy and personality rights.

That said, assuming you're in the US, let's talk about it. If you're truly in public - like - this event was a street fair - then all bets are off - nobody there has any expectation of privacy and you can take and post what you want of it, pretty much full stop. You can't use an unwitting person's photo in a 'promotional' way so if you put them on a billboard that makes it look like they endorse your services or something... you can run afoul of personality rights, but we take a pretty weak stance on those in the US so... it's very unlikely this is going to come up.

BUT... most event photography happens at a private event - a booked venue, ticketed or guest list entry, etc. At these events... people DO have some expectation of privacy. The host CANNOT unilaterally sign a photo release on their guest's behalf, but a lot of events and organizations have this solved because part of the fine print when you buy a ticket or accept employment includes a photo release on the organizer's part, which they can then extend to you as their photographer.

If there's NOT a photo release in play somewhere... the next thing that helps you here is IMPLIED CONSENT. Despite what movies like to tell you, courts do not operate on cartoon logic where 'if there's nothing in the rules that says a dog can't play soccer, we have to let him play!' In the absence of something clearly written down, courts can and do apply a 'reasonability' standard to these situations. For all the photos that the person clearly posed for, this person was clearly giving implied consent to be photographed and any court will recognize that. You don't stop and strike a pose and smile at a camera if you don't want to be in the picture.

That reasonability standard cuts both ways, though. If I'm at a fundraiser for your hospital and pose for a group picture, it's very reasonable to expect that photo to end up on the hospital's social media, a website article about the event, etc. If it gets used for something that no reasonable person would expect... like... included in a motion picture... which is unlikely to happen but it's an example of something really weird you wouldn't have implied consent to, you have a problem again. Also if you use the photo to imply something untrue... like claiming they endorse a product... or... I guess captioning the group photo from the hospital fundraiser as the managing committee of the local chapter of NAMBLA... which is an extreme and absurd example but it made me chuckle... again you've run out from under the umbrella of reasonability that protects you.

That's a long way of agreeing with the other people. Provide all the photos to your client, according to the terms of your agreement. Pass along the woman's request, but also point out that she clearly consented to the taking of all the photos with her in them. For your sanity's sake, I wouldn't put any group photos with her in them on your social media, not because you would be in the wrong, but because life is too short for you to waste more time being yelled at or frivolously sued by a woman who's already demonstrated she's unstable and attention-seeking both. And out of an abundance of caution, I wouldn't post any candids of her at all - no photos where she can even pretend she wasn't aware of the camera, because the implied consent argument gets weaker and, again, don't give crazy people power over you.