You can checkout if she needs to file a return, by looking at her total gross income (including the gambling income), but it sounds like she still won't be required to file ; if none of her SS has been taxable. Often a portion of her social security may be taxable with additional income, so you could enter her info in TurboTax and see if any/what amount is taxed (you don't pay for TurboTax online until you file).
A single person, age 65 years or older, can earn up to $11,900 before they're required to file a return. This amount varies slightly based on age and filing status (Married, single, etc.), which you can checkout at the FAQ linked below. If there's any self-employment/1099-misc box 7 income, then the amount decreases to $400 (regardless of age or filing status).
If you're claiming her as Dependent, this reduces these amounts and she would be likely required to file because she had unearned income (gambling) of more than $1,050. There's a link included in the FAQ with more info on these guidelines. https://ttlc.intuit.com/replies/3302274
If she is required to file, you can enter the Gambling winnings (losses most likely won't be deductible, but you can enter them afterward income to find out), by following the steps at the following FAQ: https://ttlc.intuit.com/replies/5122514
