Is the petitioner sinful if she dedicates her supplications to herself, her parents, and her siblings for good, and refrains from supplicating for people who do not show her affection, knowing that she will not supplicate against them with evil, and is it a condition to supplicate for others to attain the pleasure of Allah?

You are not obligated to supplicate for them, and you do not sin by refraining from it. However, your supplication for them is a tremendous good, and countering their evil deeds with kindness is a characteristic of perfect believers. Moreover, you are a winner if you supplicate for them, for the angel will supplicate for you with the like of what you supplicated for; as the Prophet, peace and blessings be upon him, said: "When a man supplicates for his brother in his absence, the angels say: 'Amen, and for you the like thereof.'" Narrated by Muslim. The advice is to continue supplicating for yourself, for them, and for all Muslims with goodness.