Sole proprietorship with one client

[mackman55]

Hi Guys, my sister is currently working in the US. She is planning to come back to India during the month of March and work for the same company but as a client. Is it legal to work with one client by registering as a sole proprietorship? Also, can she request for reimbursement for all the expenses as her company has agreed to the terms? Also, in the future, there is a possibility to hire a few more people to work under my sister. Can she hire them under her proprietorship company as a contractor to work for this one client