Sorry to hear of the circumstances.
If the low mood was treated for a prolonged period (in excess of 12 months) then unfortunately is not an appealable condition. In addition, if there was more than one incident of self-harm, that in itself is unfortunately an outright bar and non-appealable.
The alcohol aspect depends on the individual circumstances but if things came to a head in 2015 and have only recently been addressed, it could well be the case that the condition is deemed chronic (long term and/or recurrent).
The rough rule of thumb for mental health issues is the individual needs to be free from treatment (medication/counselling) for a period in excess of three years before they can re-apply, with evidence of the three years free from treatment. The period required "treatment free" is to confirm the condition is resolved as best possible and unlikely to recur - in the case of alcohol and low-mood, the period of rehabilitation cannnot usually be appealed as it is a non-negotiable mandated period.
Generally to appeal, in cases such as this, there has to be qualified medical evidence of an incorrect diagnosis or a mis-diagnosis and treatment.