I went to sem for years, both in eretz YISRAEL and the US.
There is a lot more adjustment that has to take place going to Eretz YISRAEL: language (learning Chumash is not knowing how to speak ivrit), planning places for shabbos (it can be a hassle and worrisome, not knowing where to go when the dorms are emptying out and you’re not accustomed to calling and asking to be someone’s guest)….
There might be things that you can do to ease her transition. If you have relatives/cousins in aretz, maybe you can reach out to them to invite her. My parents have tons of cousins there, but I was too uncomfortable asking to be someone’s guest. It’s just not done here, and girls may have a hard time taking your word for it that it’s normal there. I disagree with the whole “cold turkey” concept. Sending a child to eretz YISRAEL does not mean abandoning them and forcing them to learn to make do. We don’t go from zero to 60 in two seconds flat. Give her the tools she needs to manage. Her tears and fears also do not mean you have made a mistake, either. I would not be quick to respond at this point. Wait it out at least till mid winter break. That will give her a chance to try to make friends, go on tiyulim, experience yom tov in aretz (incomparable to anywhere else)…
Both you and she will always wonder, if you don’t give it enough of a chance.
I know of someone who’s father paid thousands of dollars for dental school for his son, only to lose it several weeks into first semester when the son dropped out and switched to an actuarial program. That’s part of parenting. We don’t know what investments will bring returns, but we have to try.
This is the wrong time to expect gratitude from her. She’s busy trying to adjust and tending to her own needs.
My older sister, a’h, never went to sem in Israel, because my parents thought sending a daughter away inappropriate. They later realized how much she wanted to go and that it was commonly done and sent her for a summer there. It was NOT the same.
No matter how terrible you feel about her concerns, project a positive attitude. Listen to her, empathize with her, and finally, model a healthier coping attitude that includes delaying decisions, allowing problems a chance to become resolved, and expecting good things to happen.