Sorry to hear you are going through this, OP. You say your DD has no professional help at the moment - has she ever had any, or would she agree to seek some?
I hope my experience might be helpful to you. DD (nearly 20) had a very rocky two or three years from the age of 16 which included some of what you describe, and more, and was diagnosed with Borderline Personality Disorder. We too had assumed that her apathy and low mood were just normal teenage behaviour.
I learnt that there is nothing you can do to make a depressed person (especially your own teen depressed person) do anything they don't want to do, and trying to push them is in fact the worst thing you can do.
Hard though it is, all you can do is listen to her (if she will talk to you) and empathise. Validate her feelings - eg. 'I can see that you are feeling so tired today that it's too much effort to get up and have a shower' rather than coming across as judgmental (this is so hard, I know). The complaints about friends upsetting your DD particularly strikes a chord with me, and I realise that I would brush off this kind of comment, trying to reassure DD that they didn't mean to upset her. It would have been more helpful to her if I had acknowledged that her feelings were real (however irrational they seemed to me).
Put her in control of her illness rather than trying to carry the burden yourself. As she is over 18 she will have to take responsibility for seeking treatment, but you can offer to help her to find the best route to it.
Above all, look after yourself. The airline instruction to fit your own oxygen mask before helping others is very appropriate here.
I hope your DD will want to pursue her dreams eventually. It's so sad to see them deliberately sabotaging what they and we had expected for their futures, but I really believe that with your loving support - and hopefully some external help - she will turn her life around when she is ready.