Is Blue Coat (Liverpool) a good choice?

So my sister is starting her A levels this September, she got an offer from Blue Coat; however, she says that if she goes there, her chances of getting into Oxbridge will be lower since most of her classmates will be more or less on her level academically. She also says that the teachers there are supposedly all horrible and it's only because of the students that the school is doing well.
She has her eye on another, new, school called Life Sciences UTC.
I'm not really sure about her logic when it comes to Blue Coat. I mean, on one hand it makes sense, but on the other, it's built on assumptions. What do you think I should do?
Btw, she'll be needing a more lenient system for maths as she's going to take extra modules.