Looking for a book about werewolves I can’t think of the name for the life of me

It’s about a girl who is turning 18 and she’s excited about meeting her mate because the pack is always bullying her, her brother is friends with the alphas son on the night of her 18th birthday she realized that her mate is the alphas son but he pretends not to know what she’s talking about because she’s not his ideal body type so she calls him out on it but her brother trying to fit in takes the alphas son’s word over his sister and sends her home for causing a scene feeling betrayed and alone she emails her online friend and he tells her to leave home and go to his pack not knowing he’s an alphas son too she excepts and leaves, leaving a letter for her brother that she’s leaving years later she’s her friends beta and his best worrier one day her old pack asks her friends pack for help training their worriers because they’re the best and having a rogue problem not knowing she’s gonna be the one training them.