Does the ruling of "whoever abandons his brother" apply to one who apologized to her friends for a mistake, but they did not accept the apology, and does this prevent her from receiving forgiveness?

What you did, apologizing to those you wronged, is religiously commanded. You must continue to try to reconcile and seek forgiveness until they are pleased, initiating the greeting so that you may be the better of those who have cut ties. Injustice is strictly forbidden, and the wronged person should forgive to attain the reward of those who pardon, as Allah Almighty says: "And hasten to forgiveness from your Lord and a Garden whose width is the heavens and earth, prepared for the righteous who spend [in the cause of Allah] during ease and hardship and who restrain anger and who pardon the people - and Allah loves the doers of good." We advise your friends to forgive you, for whoever is apologized to and does not accept, a great sin falls upon him.