Coronavirus: Is this employee a ‘long-hauler,’ or abusing leave?

Q: “An employee said she had Covid-19 back in the summer. She was out of work for three months. We paid her. She came back with a note saying she could return to work part-time. She said it would only be a few months. Since then she is always out sick. She has just moved to full-time work because she was set to lose her benefits and paid time off only working part-time. She now claims she has Covid-19 again. Can I request some form of proof? What are our rights as an employer?" – Nikkie, Florida