I've often checked in my wife's bag, in her absence, both when travelling / not travelling with her. I do need her passport and boarding card (either printed or on my phone).
Does anybody still 'check-in' at the airport? Why? (Other than not having access to the internet)
If there is an issue, ask the agent to hang onto the boarding cards/passports while you call your bride to attend. The agent can deal with the next customers until your wife appears and a quick check and your done.