Given my personal experience with on-line meetings and difficult child's, I may be thinking a little overboard here.
1. Tell difficult child straight up what your feelings are and why.
2. Contact this 19 year old, remind her that your daughter is a minor at only 14 years of age and explain to her that if she tries to make any further contact with your daughter, whether in person or via computer or telephone, you will call the police, who will then bring in the FBI. Be firm and tell difficult child your plan. She needs to know you are not messing around and that her romantic relationship with an adult of 19 is illegal.
2. Pull plug on this website and take away camera. Tell difficult child that you are doing this. Do not HIDE it. Either give it away or throw it away. No need for cameras ever at all, period.
3. Tell difficult child that she needs to broaden her base of places to meet other kids her own age, whether it be through a PT job at a local farm, at camp, volunteer work, youth group, gymnastics, dance, pottery, painting classes, drama school, whatever. She needs an outlet/place to meet other kids, not just gay or lesbian kids on line. She needs human contact - of the platonic kind and not all gay/lesbian - it's a big world out there and she is only 14 after all. While I don't have a problem with her exploring her sexuality at 14/15, she should be doing so with other teens her own age and not all about physical contact.
4. Yes, prepare for battle, but do not engage in battle. Be very matter of fact - do not say anything or threaten anything that you are not willing to follow through on. It will be difficult to change things up since you've allowed what you've allowed thus far. But you are the parent and you've allowed things to get this far until she spotted trouble and now it has to be changed up a bit - tell difficult child that. It's allowed for a parent to change the rules once a parent spots trouble and this situation is trouble. Period. No need to explain yourself or motives too much.
Begin to make plans for yourself outside the house or inside the house without difficult child. When you make those plans, plan something appropriate for difficult child so that she is not unsupervised.
Do not allow yourself to be held captive by the idea that difficult child may hurt herself in some way. If she does, she does. There is no way for you to stop it. It is unrealistic for you to be policing her 24/7 and it won't work anyway. I know because I tried and it didn't work. My difficult child still tried to hurt herself, she still ran away, there were still battles. Remember that you are not her buddy. You are her parent and her teacher. You love her and it's your job to broaden her horizons at this age, guide her and love her, show her the ways of the world, but also allow her to explore on her own, with care and safety. You cannot protect her all the time - you have to trust on some level that you've taught her to protect herself. So, be firm about this, but also realize that she will likely get herself into some messes you can't get her out of. And it's nobody's fault. It's just a part of life and growing up, learning.
I will be praying for you for strength, courage and determination.
