Taxability of foreign income earned outside india by R-OR

Dear All,

I have one query. My friend who was working from Dec 2019-March 2020 in Korean Airline in Korea but she is appointed by US  company because of some restrictions imposed by government for no.of employees employed from outside. She is having letter from US company about salary and tax deducted for F.Y.2019-20. She has filed return based on US DTAA Clause 25 and claimed relief under section 90/90A. Now she got demand where assessing officer is not considering relief. Return is processed in Dec 2021 with Demand  now there is no option to revise return. We has requested for rectification but  there is no change in order.

Kindly advise.

Thanks in Advance.