You may be able to find it on a tax return if you claimed your child as a dependent. Otherwise you will need to contact Social Security for help and a new SS card for her.
https://ttlc.intuit.com/questions/3355524-when-does-access-to-my-prior-year-turbotax-online-returns-...
https://ttlc.intuit.com/questions/3404575-how-do-i-access-my-prior-year-2017-return
You can get a free transcript from the IRS:
https://www.irs.gov/individuals/get-transcript
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
