The girl could have done it better. She should not have sat on her father's lap putting her full weight knowing his condition. She could have sat very lightly putting a little strain on her legs. After all the whole exercise is over in a few minutes and a little pain on the girl's part could have saved her father the trouble. Need is for common sense.
Why do we need to cling on to this outdated habit anymore? It does not matter when both the girl and her father are happy about this and don't have any problem with it. But the main point is when this particular custom comes as a great inconvenience to girls who have lost their father.
How many girls will find it comfortable (in mind) to sit on one's சித்தப்பா or பெரியப்பா's lap let alone feel "proud" about it???