That’s a good way to state it. Include something like, “if we can at all afford it.” Boarding school admissions staff know very well that FA families must be realistic.
Just don’t send such a letter to more than one school. You may laugh, but…
But then, remember that kids change. Do not send such a letter if it’s only your opinion. Make certain your daughter is serious about her ranking. It’s a serious step to send such a letter.