I am sorry that your mother is suffering from this depression
for the last 8 years. The fact that she is getting it every year or almost every year shows that it is a genetic disorder and so she has to be prevented from this recurrence bur cannot stop it altogether. It is like diabetic that cannot be cured but can be prevented by drugs.
I find that she is on the correct drugs but the mood stabilizer is not being given . There are a number of drugs to prevent this recurrence like Tegretol
, Valporate etc . If she is given them in the correct dosage ., you can prevent the next years recurrence.
This disease of recurrent depression has a great tendency to occur at the same time of the year and so it is called SAD. which means Seasonal Affective Disorder