It doesn't matter how long she was an active participant in a 401(k) plan in 2020. If she was an active participant in a 401(k) plan at any time in 2020, she is an active participant for 2020 and the deduction for your and your spouse's traditional IRA contributions for 2020 will be subject to limitation based on MAGI. Active participation in an employer's retirement plan is indicated on the W-2 issued by that employer by the marking of box 13 Retirement plan.