No way she has lost that much weight as a slim person anyway JUST by not eating much due to grief.
She is asking for your help and support I totally agree.
If this were my dd I would not be messing about, I'd be going to see her ASAP and either bringing her home or or leaving until I was TOTALLY Confident the genuine cause was being properly addressed by professionals as well as dd and that she was getting full support from uni too.
It could be an Ed, which I think is the most likely explanation, I don't think grief would necessarily have triggered it I suspect it was already an issue and the grief worsened it.
But it could also be a sign of a physical illness that's going missed cos everyone around her is assuming it's due to the grief. That needs to be ruled out as that is a very significant weight loss in a short period of time. Such conditions are thankfully rare but they can happen.
She needs a thorough assessment and to be referred to the appropriate professionals depending on the identified cause
How was the counsellor found? Because also that's not a protected tote in the Uk, literally anyone can call themselves a counsellor and "treat" people - but if they haven't the knowledge or experience to deal with an Ed they could well do more harm than good.
Eds are among the more dangerous mental illnesses and it really is better to get them identified and treated ASAP.
I've known a few people with them (thankfully escaped myself so far - I have ocd with some food based thoughts which could tip that way if I weren't careful) and I've seen the harm even a qualified mh professional without real experience of Eds can do it's an incredibly tricky condition to deal with.
Do not take a "wait and see" approach with this, your daughter needs you go be with her and support her to get whatever help it is she needs.