@ClareBlue
The BF is using emotional manipulation and your daughter has no experience in dealing with it. Those saying she is 18 and it is all her choice are wrong. We can all be vulnerable at any stage in our life and those close to us should support us, especially parents.
This is different to interfering or controlling our children or their lives and most parents recognise it is a difficult balancing act to get right. One way to help is by sharing experiences.
As
ClareBlue says
When she is abroad, in a villa, in a country where she doesn't speak the language she is very vulnerable.
When she is there I don't doubt the boyfriend will be pressuring her for sex (which may not have happened between them yet) and she won't have anyone to fight her concern if she doesn't want to go that far (or do particular things).
I know this sounds controlling and dreadful but I'd be tempted to hide her passport!
The problem is that if you come down hard, she will go just to spite you and show you she can do what she likes. Have you met this boy? What is he like? Can you use worries over the pandemic to talk her out of the holiday - and that fact that she'll be missing college?
If she's come home crying about what he's said, that suggests to me that in her heart she doesn't believe it but is frightened of losing him. I don't think she really wants to go, but can't see a way to refuse (she is a "young" 17 and the family sounds "pushy" at best). You could point out that he says that you are controlling, but he is also putting pressure on her, and if he cared about her he wouldn't want to make her unhappy. (And also, that he doesn't seem to be able to do anything without his parents holding his hand all the time. How is that not controlling? TBH, I think it's weird) But I honestly think it's likely that she doesn't particularly want to go but can't think of how to say "no".
I agree that expressing disapproval and then backing off is the way to go. Maybe point out that if he snaps at her like he did today, she'll be stuck with him and 2 adults who will take his side, 2000 miles away.
I think this is the only advice you can give - and point out that if she becomes ill then there will be no National Health Service there, and that the destination's own medical services are likely yo be overwhelmed, too.
And pray for a foreign travel lockdown.