FSA for babysitter

Hello, I have $5000 taken out of my paycheck pretax every year for dependent child care expenses.  This school year because my children are distance learning I’ve had to hire a babysitter.  I pay approximately $800/month.  I tried to submit for reimbursement from my FSA but they are asking the babysitter to sign a form verifying her services.  She’s 19 and doesn’t want to sign.  What am I supposed to do?  How can I get reimbursed?