It is a risk but it's fine to travel, take care, be a responsible adult.
This family is looking for someone to blame, it's clearly the daughter's fault, she was probably out partying, having a good time socializing before her holiday to Thailand, when she should have been in a bubble keeping herself clean before traveling.
If you take the risk, traveling in these covid times it can be a costly mistake, if you become infected, minimize your risk by keeping away from others.
Be accountable for your actions, stop blaming others.
Now, the sad photo of her, we all need to feel sorry for the 18yo.