Actually both options are possible here in the Netherlands, it's a matter of preference of the patient. In both cases a doctor will be present, whom will also supply the drugs if a patient chooses to take them themselves.

This case is incredibly rare though, it is already extremely hard to have a euthanasia request granted for mental issues at an older age, let alone someone so young.

A bit more background on 'the aftermath' by the way, as the article doesn't mention that: after the euthanasia has taken place a coroner will establish that this was indeed the cause of death. Once that is done the public prosecutor needs to give permission before the remains may be buried or cremated.

Also, the coroner will send the report of both the physician who approved and performed the euthanasia and that of the SCEN-doctor, who performed the obligatory 2nd opinion mentioned in the article, to a special committee that will check if everything went by the book. Not only the procedure leading up to the euthanasia, but also the act of the euthanasia itself. If there are doubts about whether or not all means of treatment were exhausted and if there really was undue and indefinite suffering, or if there are any doubts if the patient really wanted to go through with the procedure at 'the moment supreme', a doctor can be held accountable for that. Fortunately that is rare, as the whole procedure is not taken lightly.