Okay, well, the fly absolutely has to walk the thirty feet of the length of the room. That is not negotiable. The trick is in how it gets to the length of the room - by wall or by ceiling.
The fly therefore has two routes:
Route1: Walk directly sideways along the wall to the corner (six feet), maintaining its one foot above the floor at all times. Turn and walk along the length of the wall (30 feet) until it reaches the next corner and walk to the sugar lump (six feet). Thus, the fly has walked 6+30+6 = 42 feet.
Route2: Walk directly up the wall to the ceiling (11 feet (the wall is 12 feet, and the fly is already one foot off the floor)). Turn and walk along the length of the ceiling (30 feet) until it reaches the next corner and walk down to the sugar lump (11 feet). Thus, the fly has walked 11+30+11 = 52 feet.
Therefore, it is quicker to walk along the wall.
Now all we have to do is establish whether Jane broke the fly's wing in order to test a mathematical problem (in which case, she's a sadist) or whether she's trying to encourage the fly to get better by feeding it (in which case, she's an oddball).