I understand your situation, but there are months to go until July and circumstances can still change. I presume you must have HSFG, SHS or RH as a secure place? These are all really good schools too.
From your info I would say your daughter is 8th on the waiting list, but that could be higher if some in the original 135-141 (i.e. just above your daughter) did not put it on their CAF in October.
One point about the admissions office: they probably don't want to put people's hopes up or give false information rather than be deliberately obtuse or cagey. They usually have other jobs within the school (receptionist, exams officer, PA etc) and are busy people. Also add in the 100's of questions they must get every year: those within top 180, those who have got place but want to visit the school again to "check it is suitable" those who got a high score but probably just outside 180, those who wish to appeal...... their phone is probably red hot with callers!
I do think that only 2 dropping out in March does seem very low, but it is possible this maybe the case this year.
Sorry I can't give you more definite answers, but try and stay positive. As I said before, if you have one of the girl's grammars as your chosen school then you shouldn't be too downhearted.