Yevamot 104 - Which part of the leg is good for chalitzah?

If a part of one's leg, up until the knee, has been removed, he can still do a valid chalitzah; however, if it was amputated above the knee, this chalitzah is invalid. But this does not seem right! When one goes to Jerusalem on a Festival, such as Pesach, Shavuot and Sukkot, which are also called "Regalim," to indicate that one goes on foot, only people who have feet ("regel") have to go, and one with prosthetic foot does not. This tells us that "regel" is a foot, and without it chalitzah should not be allowed! - No, chalitzah is special: since Torah says, "From above his foot", " Me-al regel ," this tells us that the part of the leg above the foot but below the knee is also included. But if so, let's include also the thigh! - No, the thigh would be "above above" the foot, and that's too much.

And yet, there are five places where thighs are also called "regel," such as in the story of Yael. When general Sisera came to her tent, and she offered him "milk in royal vessels," he subsequently had intercourse with her seven times, as indicated by the verse " He fell between her feet (regel), bent, fell, lay ..." where the variation of "fell" is mentioned seven times. So thighs are also called ("regel")?! - No, in truth thighs are not called "regel", but here it was done for propriety, out of respect for the righteous Yael and her deed, weakening Sisra and killing him in the end.

Incidentally, why does Yael deserve so much praise? Granted, even though she was a married woman, yet her transgression was a permitted, and even righteous deed, since she intended to help the whole Jewish people. Still, she derived some pleasure from the act!? At least we should remove the words "More praiseworthy than all women (meaning Matriarchs) is Yael!" - No, since we have a rule that even a minor benefit from the wicked is abhorrent to the righteous, it can be said that Yael derived no pleasure whatsoever.

Art: Yael and Sisera by Artemisia Gentileschi