Bulimia-how to help my 18yr old daughter

[Worried1mum]

my daughter is binging and purging, at the least this is happening every evening, I am not sure how often each evening as she is quite secretive about it. she has lost quite a lot of weight 2-3 dress sizes. she was unwell a couple of months ago and I think maybe the persistent cough was making her gag and be sick and the cycle has continued from there.
She has a history of cutting herself and had counselling and she appears to not have relapsed into that. She knows I know and I am trying really hard to keep out limited venue of communication open or she does have a tendency to shut everyone out, I try not to nag her about it but I really feel she needs some help, if too much pressure is applied she will just cut herself of and the depression will become deeper.
How do I help her get to the right place to have the confidence to see she needs help to deal with this and then take the step to get that help?

[Worried1mum]

Any one, any advice or ideas?