I am planning to get married this year and AFAIK my filing status next year will be either 'married filing jointly' or 'married filing separately'.
I see most of the instructions/articles talks about apply for INIT along with tax return.
For my foreign fiancée whom won't come to U.S anytime soon, can I apply the INIT abroad for her first via IRS agency so that next year I can just file the tax return and skip the INIT application process?
Or it's recommended to apply the INIT along with tax return?
No, the IRS won't issue an ITIN without a tax return to apply the request to.
And that return must include the person asking for the ITIN and must have a reason for them to be filing.
If you get married and decide to file Married Filing Jointly, you must also include a statement making that election with the first year return (as well as the application for an ITIN) so plan to file early next year.
TurboTax will supply the statement with your tax file if you select
"My spouse is a nonresident alien or dual-status alien spouse"
and
"Would you like to treat your spouse s a U.S. resident for the entire tax year?" YES
There is also a "Learn More" link embedded in the software the explains the process and how to apply for an ITIN.
The IRS has Certified Acceptance Agents who will verify your identifying documents in person, which seems safer and faster than mailing the forms.
HERE is an IRS link with more information
HERE is a TurboTax link with more information