This is so typical of a female parakeet. She may be scoping out the bowl as a nesting site. First, make sure you have at least two food cups at different places in the cage so that both birds get enough to eat. She might be trying to "claim" one bowl for herself. You can look into the type bowls that have a hood over them & this may help. Another idea would be to place a shallow dish under the bowl so that the food lands there instead of falling through the grates. Parakeets are mostly ground feeders in the wild, so you might just try using shallow plates on the cage floor for them to eat from. Be sure they are not placed under perches. Offering less food at a time can also help. Parrots are foragers so when they have a lot of food, their instinct is to eat a few choice bites & discard the rest. This is fine in the wild as it replants & also feeds ground dwelling creatures. But it is just an annoying waste when our pets do it. By giving them less food at a time, they may eat more efficiently. If you give them a lot & they know they will just get more if they throw it, then they will never learn. You can also make a point of placing the tossed food back into the bowls as long as it didn’t land in poop. There will always be some waste with pet birds but maybe some of these suggestions will help cut back on the waste.