Did she have any income?

$17 in interest & $367 in dividends - So she files?

If she had income yes she would need to file

$367 is capital gains.  $17 interest & $116  Qualified Dividends

you say your father died during 2015, so your mother should have filed Married Filing Joint for 2015, widowed/ single  for 2016 --- and are you saying that her  total world income is only $367 capital gains, $xxxx total dividends, $116 Q-dividends and $17 interest income ?  How does she live  -- did she have social security, IRA or pension from your father ?    Do you supprot her  or what ?

& her Social Security

If that is the totality of her income -- Interest income, Dividend income, Social Security  -- then she may not have to file because her taxable income after standard deduction and exemption would be  ZERO ( negative ).