If you originally filed Joint that is one return.  You amend it to be single for the primary taxpayer listed first on it.  Did you take off all her info?

Then she has to file a new original return (not amended) as Single for herself.  Https://ttlc.intuit.com/questions/1894512-how-do-i-start-another-return-in-turbotax-online

@keagwa - You *cannot* simply amend a joint return to single - that is not allowed because after the due date of a tax return neither spouse can disavow themselves of the joint liability on a joint return.

Filing a joint return when you are not married is a very special case and requires the IRS to declare the joint return an *invalid* tax return.  Doing that is definitely not do-it-yourself and requires professional help.  Even many professionals do not know the procedure that is defined in the IRS  Internal Revenue Manual (IRM).