If your spouse has more than 24,800 of itemized deductions you should file Joint and take the itemized deductions. If she files separately and itemizes then you must also itemize your deductions even if your deductions are less than 12,400. Even if they are zero. So you would not get the Standard Deduction on your return.
Can your spouse deduct all their deductions? Some deductions are now limited. There is a limit on SALT deductions. SALT is State And Local Tax. Which includes property tax, any state tax paid like for last year’s return and includes any state withholding from your W2s and any 1099s you have. And any other taxes like in W2 box 14 & 19. You can only deduct up to 10,000 (5,000 MFS) for SALT State and Local Taxes.
FAQ on changes starting in 2018
https://ttlc.intuit.com/community/tax-reform/help/how-will-tax-reform-affect-my-federal-tax-return/0...
And some Deductions that have been suspended for 2018-2025
https://ttlc.intuit.com/community/tax-reform/help/which-federal-tax-deductions-have-been-suspended-b...
