She would probably accept this practice because she would be trained to believe it was normal. Also, people in this community are devoid of emotions, so there is no reason that she would consider the practice cruel or merciless. While Fiona is painted as a sweet, caring, and kind girl, this only adds to the sad fact that even the most congenial of characters can become doers of evil in a society that controls their citizens' every move.
Lowry shows throughout this book that each character is capable of falling into evil. Perhaps the most important of these illustrations is that of Jonas' father "releasing" or murdering an infant because it was born weighing less than his twin brother. All characters are capable of doing horrible acts, all in the name of doing their jobs in the community.
Fiona accepts the practice of releasing the old because she has been raised to think that being released is a beautiful and normal thing. At one point in the novel, Jonas has a conversation with Larissa. The exchange tells readers some important details about releasing the old. Larissa tells Jonas that earlier in the day, they celebrated the release of Roberto.
"This morning we celebrated the release of Roberto," she told him. "It was wonderful."
Notice the use of "celebrated." There are several other times throughout the book when Jonas describes that the release of the old is a celebration of their life. Fiona has no reason to not fully accept releasing the old. Releasing old people is not only normal, but the practice is also celebrated. Fiona has been conditioned to believe the practice is a happy and good thing.
Additionally, the Sameness has basically deadened everybody's emotions. People can talk about being happy or sad in the novel, but it is clear that they don't really understand or fully experience either emotion. Fiona doesn't have any negative reactions to releasing (killing) people, because she isn't capable of experiencing those emotions.
Because she knows nothing about death, also they have no emotions. she has no idea of wat she is doing, and she thinks release is a good thing, but really, it's not.
because the community has no emotions and she has no memories of death. she has no feelings or anything. she has no ideas what she is doing she dosn't really understand what release really mans. to her it is just the name of releasing someone. she dosn't know what death is and was trained not to