You should not have reported her stock sale and loss on your tax return. You will have to file an amended return, for yourself, to remove that transaction and the effect it had on your bottom line (the loss most likely reduced your tax).
As for her return; you do not report his/her income on your return**. If it has to be reported
at all, it goes on his own return. If your dependent child is under age 19 (or
under 24 if a full time student), he or she must file a tax return for 2016 if
he had any of the following:
1. Total income (wages,
salaries, taxable scholarship etc.) of more than $6,300 (2016).
2. Unearned income (interest,
dividends, capital gains) of more than $1050 (2016).
3. Unearned income over $350
and gross income of more than $1050
4. Household employee income
(e.g. baby sitting, lawn mowing) over $2000 ($6300 if under age 18)
5. Other self employment
income over $400, including box
7 of a 1099-MISC
Even if she is not required to file a tax return, there are two reasons, you may want to do so anyway. If the 1099-B was large enough it could be a red flag to the IRS and you may want too head off an IRS inquiry. Although she does not need to file a return to have a capital loss carry forward to 2017; the actual preparation of a return is the most accurate way to calculate the carry over.
**If her only income is from interest and dividends, Alaska PFD or capital
gains distributions shown on a 1099-DIV, there is a provision for entering
it on your return, using form 8814. But, since she has 1 1099-B, you cannot do that for 2016.
