Yes, you can file your Federal Return jointly.
If your wife considers Kansas as her Resident State, she could file a Resident return to Kansas separately, as you suggested, and report all of her 2019 income there. She will get credit for any tax she paid to Oklahoma.
She can file a Non-Resident Return to Oklahoma, reporting only her income earned/taxes paid there.
Click the link for more detailed info for filing Non-Resident State Returns.
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