Is it a sin to distance oneself from a committed and beneficial female friend due to the parents' unawareness and fear of problems?

There is no obligation to inform or seek permission from the family regarding communication with a girl. It is permissible to continue communicating with her as long as it remains within the bounds of what is Islamically permissible, and there is no sin in ceasing communication. One should utilize communication in a way that benefits one's religion and worldly life, avoid wasting time, and prepare for the Day of Return, in accordance with the Almighty's saying: ﴿O you who have believed, fear Allah. And let every soul look to what it has put forth for tomorrow - and fear Allah. Indeed, Allah is Acquainted with what you do.﴾ and His saying: ﴿O you who have believed, fear Allah as He should be feared and do not die except as Muslims.﴾ And according to Ibn Mas'ud's statement regarding true piety: "That He is obeyed and not disobeyed, remembered and not forgotten, thanked and not denied," and according to the Prophet's (peace be upon him) saying: "Two blessings in which many people are deceived: health and free time."