It's possible. First talk to her doctor, and make sure she is probably fit enough not to keel over half way. The airline may ask for this anyway. Then decide on the route. If it's at all possible, have a family member accompany her, to help with bodily needs, getting to the hotel, etc. It is best to break the journey into stages with flight during the day, a night or two in a decent hotel between each flight. You really don't want her sitting still for more than seven or eight hours. Consider going business class anyway, with a lie flat seat. Obviously book assistance at all airports and hotel transfers. You won't want to be leaving her by the exit while you are looking for a taxi. Oh, and use incontinence pants or pads for her if you think it's possible that she will have a problem. You might need to be very tactful here.
But on the whole, it's possible. Full time wheelchair users travel by air, after all. On their own. Most of the reasons for traveling with her are down to her doing something new at an advanced age, and giving her moral support.