Notice u/s 148

My mother has received Family Pension of Rs 35000 per month from 2011 to 2016  but was not aware of the tax implications on it, therefore she never filled ITR of any of the FY.

Now the Income Tax department has issued notice u/s 148 and told her to file return for AY 2012-13.

My Queries is:

1. How much tax she has to pay now along with penalty (if only pension amount is considered) for AY 2012-13.

.