Why am I having so much trouble forgiving this person?

I don't think I ever had trouble forgiving people, it always came easily to me but this one person that promised me she was a safe place, lied to us and told me my disabilities doesn't exist and then posted it online for people to make fun of me and made us homeless, made me suffer It's been snce March i still can't forgive, not like she will ever say sorry but i usually don't need someone to apologize to forgive them but this time. I can't understand this, I have forgiven people that almost killed me, I have forgiven my mother for all the bad stuff she did and abandoning me but I can't forgive this one person