Is my spouse who entered the US on April 2, 2019 on a K1 fiance visa required to report all of her financial income from Russian owned bank accounts on our joint returns?

If your spouse is a "US person" for tax purposes, they must report all their world-wide income and pay US tax on it.  They can claim a deduction for taxes paid to a foreign country.

A "US person" for tax purposes is a US citizen anywhere in the world, a resident alien (Green Card holder) anywhere in the world, a non-resident who is in the US more than 183 days, or a non-resident who is treated as a resident in order to file a joint return with a spouse.

I am not specifically acquainted with the K-1 visa, but if you are married now and filing a joint return, then your spouse is probably considered at least a resident alien and must report all their world-wide income.

Note that money someone owns in a foreign bank is not by itself income; the income is any interest or dividends the money earns.