Is a daughter considered sinful for disobeying her parents and performing the 'Isha prayer before going out, fearing death or an accident before performing the prayer, knowing that her intention was not to disobey her parents?

It is permissible to perform the prayer at any part of its designated time. If someone intended to perform it and then died during that time, they would not be considered sinful. Delaying the 'Isha prayer until the first third of the night is preferable.

You erred in disobeying your mother's command and insisting on praying at the very beginning of its time. Obedience to parents is obligatory and takes precedence over recommended acts and permissible matters. Scholars have explicitly stated that a child is obligated to delay prayer beyond its early time if their father commands them to do so, so that the child may pray with him.

Therefore, you must repent to Allah Almighty and strive to be dutiful to your parents and obey them in matters that do not involve disobedience to Allah.