I am really sorry to hear about your experience. I am not sure at all that it is standard practice - I certainly hope it is not . I would be very upset over that happening - my experience with indies is that they tended to write about financial matters eg bursaries / fee increases
/ extras rather than discuss them face to face and I think that would have been fairer in this case, particularly with your DD outside.
I think that sometimes when parents have been paying fees all along the school can assume that you will continue to do so in the same way - it may be that they have heard lots of stories of financial woes and can't help them all or feel they need more evidence of the financial problems (did they ask????)
Personally I would wonder if I wanted a child to stay there after they behaved like that, I can remember a teacher who used to comment to us (unfavourably) about another child - by name- in DD's class - I was stunned by this, it happened more than once and I hope the child's parents never knew, though i suspect we weren't the only ones the comments were made to. DD was nearing the end of the time there but it would have given me concerns about her staying.