What is the procedure to open a tax file in America(California).

What does it mean when you said you wanted to open a tax file for Ms. Sarker? Does it mean that you wanted to asked for her tax records? If it is, then it would be a long shot, unless the taxpayer would consent to it. You need to talk to an attorney for guidance on requesting tax records.

Not really clear what you mean here. If by opening a tax file, you mean fining a return, then that is easy (if the person is a US citizen they are taxed on worldwide income, as well as subject to a number of foreign asset reporting requirements). If you mean you want this persons tax data, you need to be eligible to represent the person and have an IRS power of attorney on file. If you don't have that it is illegal, in most cases, for the IRS to give you any information.
If you want the assistance of a tax attorney, you can search for people who can help here on Avvo and then contact them individually (Avvo does not itself represent any of the attorneys listed here, it is just a directory).

A United States citizen may have to file a US Federal tax return if she meets the income requirements, and whether or not she is an expatriate. One opens a "tax file" by having a valid social security number, sufficient income to be required to file, and then filing a tax return. Please check out the website for HRBlock, where you can find a lot of helpful information and contact a tax professional familiar with international tax returns.