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My parents-in-law used wheelchair assistance from Chennai-Hongkong-SFO. They said its was very convinient and dint have to worry about check-in, baggage claim etc also as the assistants would take care of them also. They said they were'nt even a bit tired in the travel and transit. Just make sure to mention it in the ticket. Otherwise also I think u can ask in the airport or your mother can ask at anytime in the travel for assistance, I'm not sure.