I am in similar situation. My wife got SSN in 2017. We didn’t know that we have to inform IRS to rescind the ITIN and move all income to SSN. On 2018 and 2019 return I see her ITIN is listed.
I remembered I used the SSN while filing but now we can see its ITIN on returns( can’t confirm if my mistake or it is overriden by IRS with ITIN)
We sent a letter to IRS last week to rescind the ITIN and use SSN. As we got SSN in 2017 so once IRS will update the SSN on IT returns will she be eligible for stimulus while filing 2020 returns