What is the best option for my fiance who is applying for a visa?

My fiance who is an au pair (with NO 2 year residency) applied for a COS from J1 to F1, and got a RFE for Financial Ability because her bank account showed the required $20,000 mentioned on the I-20 deposited into her account with just one month prior to sending it to USCIS. As of now, we only have $10,000 remaining in that account. When we sent the application for COS to USCIS, she had the money in her account. I have a steady job, and I can show my pay stubs for the last 6 months (not sure if that would work). Also she will be living with me while she goes to school (hence the rent issue is solved, as I will pay rent). I think our only options would be : 1) getting help from her parents (although they can't as they are salaried employees without a lot of savings, stocks, bonds, etc.) 2) Ask my boss to sponsor as he trusts me and he pays my salary every month (this seems to be the strongest possibility, as he has helped me financially before) 3) Ask her host family to be her sponsors, showing the $20,000 in their savings. I would highly appreciate it if anyone can help me in the right path. I know some might suggest going to an immigration lawyer, but we can't afford one right now.