The story about the cleaner having "difficulty moving" was an afterthought after her uncouth behavior was exposed. If she was anywhere near the cleaner, like what you just said, she could have passed it to the cleaner or left it on her trolley. Instead, she left it on a table - not an empty table but a table where a family was dining. How uncouth and rude !
If the man didn't kpkb, and if they family cleared their own trays without clearing Mdm Lim's tray, people would think that it was the family that did not clear the tray.
The truth is she was lazy but was under pressure to clear the tray "from her table" where she dined. So she conveniently moved her tray to someone else's table. When she was confronted, she conveniently used the cleaner as a cover.