"She does not want to pay SS tax on this income"

Has she ever listened to a little song by the Rolling Stones?  It goes on schedule C and she pays SS tax on it..

You need to determine if she was a Household Employee or an Independent Contractor/Self Employed.  While the fact that the worked for three different households leans towards Contractor, there are many factors involved.  What the employee "wants" does not matter; you need to determine if she was an employee or contractor.

https://www.irs.gov/businesses/small-businesses-self-employed/independent-contractor-self-employed-o...

Is this post related?

https://proconnect.intuit.com/community/proconnect-tax-discussions/discussion/4029-exemption-how-do-...

She was definitely a household employee in all 3 places.

Yes, it is.