As someone who's played tennis, that shot's real, if rather uncommon. You're actually more likely to do an under-the-leg return while facing sideways to the ball. (One leg forward, and swinging between the knees.)
If you're hit by the ball, it counts as your swing, and its your fault for not returning it, and low balls are much harder to return, so if you charge to the net, aiming for the opposing player's feet or knees is a pretty solid way to force them to screw up.
The reason Assam is so angry is that St. Gloriana is a school of ladylike elegance, and that shot between the legs (especially since her legs are spread) is about the most uncouth way to return the shot.
Like this!Which one?Some- thing like this?Umm .... Let's see...Like this... I'll do it better than the pros... I'll hit it back over!TechniqueAssamMiss Assam, I want to do that! Y'know, that!Aah... OK...Yeah, that's great!WhapSsam!Just how should I do this... Umm...