Yes, will have to pay the fees, but can't imagine that will deter them from going onto the waiting list, as one term of fees is little compared to 21 terms of fees,which is what 7 years of independent ed amounts to.
OP can go onto waiting list, holding onto the Independent school place until the point if and when she gets an offer from the grammar. This wouldn't be immoral, as isn't holding 2 places. This is exactly why the independents ask for a terms fees - as this kind of thing happens a lot. And I think that a terms worth of fees is getting away with it lightly tbh. The school might have hired an extra teacher on the basis of a few more pupils and if that amount drop out after the teacher is hired, their salary will still have to be paid whilst a few lots of 1 term of fees might not cover it.
What is OPs friend planning to do if she goes on the waiting list and DOESNT get the grammar place? Will she cough up and go independent, planning to be there for 7 years once starting, or look round for an alternative state option? Is it truly not being able to afford it (seems unlikely - why would you get to this point if this was the case) or is it just cold feet at the thought of the fees and lifestyle impacts? I suspect that if there is no grammar place forthcoming, they will cough up for the private school. Might always kick themselves though!
Is there any chance that they go on the waiting list, receive an offer again for the grammar and then turn it down again? The reasons that made them turn the grammar down first time round, may make them do it again, when it really comes to it.
OP I suspect your friend has cold feet at the thought of the cost and is just speculating to you about what she might do, but in reality has thought through her decision and will stick with it, although feeling a bit anxious. Turning down a great free place in order to pay for years is something people do after lots of soul searching, and I suspect all but the richest feel a bit worried they might have made a mistake at some point. However we make our choices and then we must live with them.
I would say that until the child starts the school, it IS possible to change ones mind, as long as one is prepared to pay any financial penalties. So if they really think the grammar would be best, they should get on that waiting list tomorrow and not hang about. If however the child starts at the private school, I think they should stick with it then.