mother is around 5'6 tall and weighs about 104kg
she has undergone many operations in her stomach so cannot do any exercises. So she gained more weight. She is not much active.
How can she be able to lose weight please advice me. I will tell her. But she eats around 1300-1600 calories a day.
Well she should at least be able to walk, so that is something, but I would say she needs to be eating slightly more calories than she is, so if she was eating around 1,800 a day, which is the sedentary average that would be better and it gives her a higher level of nutrients in her diet on a daily basis.
As for the exercise as stated she should at least be able to do some walking, as it doesn't seem, from you say, that she is extremely overweight and struggles to move, or has severe knee or ankle problems, so at least 0.5 - 1 miles a day should be something she could commit to.
Anything else you would like to tell me, might make some difference.