What is the ruling on providing a laptop to a sister if she will benefit from it in her studies, despite the possibility of it being used for unlawful matters, and does the possibility of her working in mixed environments in the future affect the ruling?

Assisting Muslims and attending to their needs is meritorious (mustahabb), and this merit is further emphasized for relatives, as it embodies righteousness and maintaining family ties. Your assistance to your sister is among the best acts of obedience, as she is a kin whose ties must be maintained. As for your concern that she might use the device for unlawful purposes, if you are strongly certain that she will use it for something unlawful, then it is not permissible to assist her, based on the Almighty’s saying: "And do not cooperate in sin and aggression." However, if it is merely a doubt or an illusion, then do not refrain from assisting her. You should have a good opinion of her, and the default for a Muslim is soundness. As for cartoon films, scholars have not unanimously agreed on their prohibition per se; rather, there is a considerable difference of opinion regarding them, so it is not permissible to condemn someone who adopts one of the two opinions.