This is certainly the right answer. Call the airline several days in advance and alert them that the passenger will require wheelchair assistance.

The assistance should be available from the curb onward - the question becomes how to get started. How are they arriving at the airport? If dropped off, try to find a seat somewhere and get someone's attention. I'd be prepared to tip a skycap to help with the luggage and let them know a wheelchair attendant is required. Or, you may be able to have an airline employee or airport staff start the process.

Once the attendant and wheelchair show up, they'll know the drill with security and such.

If this is a peak travel day, they may be short-handed. Try to arrive plenty early and be prepared for some delays. If they end up at the gate early and will be able to do the jetway without the chair, release the chair and attendant to go help others.