You need to cease all contact with this person and report her to the police and Actionfraud. You're being blackmailed and once you start sending money, that doesn't solve the problem. It just creates more of them. This is what's known as a sextortion fraud.
Sextortion stands for Sexual Extortion and extortion, of course, is blackmail. Typically the target of the scam has answered some back page ad or had been chatting with someone they met on the web. The conversation got explicit and they are coaxed into sending nude photos or videos. Then they get blackmailed with them. Pay money or they will publish the pictures or the video.
If you Google "sextortion scam" you'll get an idea of how popular this fraud is. You'll see tens of thousands of scam reports and warnings about this scam. There's no good news answer to the problem. There is only common sense:
DO NOT PAY HER ANOTHER CENT!
You should never give in to a blackmailer. They NEVER strike just once. Don't be foolish enough to think that this will stop if you pay them what they ask for. Within a day or so of that, they'll be asking you for more money and more money and more money and more money until you run out of it. And they still won't go away.
On the other hand, if you block them, ignore all of their contact and requests, call their bluff and send them nothing, there is nothing she is likely really going to do. Their only real power is in their threats. She gets absolutely nothing from exposing you.
Believe it or not, nothing she can do to you is worse than what you can do to yourself if you continue to pay her. You can live down embarrassment in the worst possible scenario. But you can't live a life giving all of your money to blackmailers. The people you hope to protect would have to learn about this ultimately anyway as you become increasingly more desperate for money, but you'll be in much worse shape then.
As many times as we get stories like this one, we have almost never seen the blackmailer follow through with the exposure she threatens. That's because she gets NOTHING she wants out of exposing anyone. All she really wants is money. If you don't pay, the odds are very high that she'll just move on to try to blackmail someone else.
She cannot post your photos on any social media site. None of them allow explicit photos or videos. They would take it right down. It's a violation of the site's terms of service. They can try to use Messenger to get to your Facebook friends, or send private messages via Instagram but you can get ahead of that by making your friends private and then contacting your friends and telling them not to accept friend requests from any strangers. Your friends cannot read her messages if they don't accept her as a friend first. If you warn them not to friend anybody, they won't be able to see the screenshot. You don't have to tell them the truth. Just tell them that you've been approached by a hacker looking to infect your machine and that they should not respond to messages from strangers or click on strange links or open attachments from people they don't know.
If she has your work email address, you can talk to your company's IT specialist and they can be on the lookout for a mass mailing with a suspicious attachment. He or she can keep the message from getting through.
So again: do not pay her. Block her. Don't read or believe her threats. She's only trying to intimidate you so that she can steal your money. The odds are 99.9% that if you ignore her, she'll do absolutely nothing. If, on the other hand, you pay her and then keep paying her, the odds are 100% that she will keep threatening and asking for more money for the rest of your life until you stop. Then every day you will still be as scared as you are now, but you'll also have no money left.
You can ask as many different experts this question as you like. NOBODY, not even your law enforcement authorities will tell you to pay a blackmailer like this. You have only one choice and that's to block and report her.
Chatting and exchanging sexual videos with another adult is not illegal. You did nothing wrong and cannot get in trouble for this. Your scammer, on the other hand, is committing a crime by blackmailing you. Block her. Don't enable her further by listening to her threats or trying to reason with her. Cease all contact with her immediately. Report him to the police, and to ActionFraud.police.uk