Max length of stay outside US on F1 STEM OPT

Hi,

My wife is on F1B VISA and currently working from India since 23rd Jan’2020. She is working from India till now and getting her paystubs regularly.

She went to India due to medical issue but not able to come back due to current situations of COVID-19 spreading across the world.

I have following queries.

  1. How long she can work form India on F1B STEM OPT ?
  2. Will there be any issue at Port of Entry when she comes back ?

Thanks,
VM