She may be right. There's a big difference between a 14yo and 18-22+ yo's. She likely will not feel that she fits in in any way. While she might be able to have a conversation here and there and it'll be okay, for the most part, she is going to have little interaction with people she can really relate to. However, this might also be related to whatever experience she previously had in public school. How long was she in school before homeschooling?
At the age she's at, I think you've got to really discuss this with her before coming to any decision. Figure out what worries you about her going to high school, figure out in what way homeschooling isn't meeting her needs (the 14yo homeschoolers I know are very active with other kids roughly their age and don't feel the need to be in school to get that social need met), discuss possibilities for changing that, make sure she has a clear view of what school is like, etc. Even hypothetically discuss how she would deal with different awful scenarios that could pop up. Take your time and let her know that you want to discuss this more than once so that you both are clear about each other's feelings and wants.
When it's all through, if your preference would still be to homeschool her and she still wants to be in school, the decision will depend a lot on her, what she's like, the likely behaviour/attitude outcome for her if you insist she continues homeschooling, etc. and what will be in her long-term best interests.
To explain further: I once met the mom of a 13yo who was in her 2nd year homeschooling. The girl HATED homeschooling; was thoroughly embarrassed by it (she complained to her mom when the mom said they were homeschooling because she said it was "embarrassing"--there were only homeschoolers around). Just by watching her and listening to her, I bet she had frequent fits and pleading sessions to be allowed to go back to public school. Yet, her mother was determined to homeschool them and was loving it. Just the way this girl *was*, you knew homeschooling was the best thing for her so that she would hopefully become less peer/superficially focused and gain some actual sense of self and true confidence.
On the flip side, I knew a girl who was an only child, single mom, the girl was quite responsible, had been in public school before 3 years of homeschooling and was just really craving some more social interaction (she didn't even really have anybody she could have called a friend), which was difficult since she wasn't driving age and her mom worked days. They talked and it was decided the girl would go back to school for her gr. 9 year. Afaik, the girl has been there for 2 years and all has been good.
A long way to say that it's going to depend on a lot of factors!