In her defense, if Patty knew what he was going to try to do she would have at least attempted to stop him or pull away. She was trying her best to keep herself guarded, doing everything she could to try and salvage what little pride she could possibly still have for herself, so Derek pulling her so suddenly into himself was something she would have said he wasn't allowed to do. She would have justified all of this to herself if she could stick to her anger for just a bit longer, but suddenly she was back in his arms and Derek's mouth found her own, and Patty melted.
She would have liked to be able to say that she had resisted a little more but it would be a blatant lie. Patty gave in almost immediately, not only returning his kiss but deepening it, and her hands twisted into his shirt tightly in an effort to pull him closer into her body. His clothes were soaked, hers were much too thin, but Patty didn't care in that moment as one hand moved to the back of his neck to try and drag him down closer. Maybe he was going to leave again. He could still change his mind and leave her to sit there and wait for him forever, Patty wasn't blind to that possibility, so pride and guilt be damned. She might not have gotten another chance, and she knew taking this one would make everything so much more horrible if he forgot about her but she needed it. She needed this... Patty needed him.
He was tall. She was struggling to keep him as close as she ached to have him, and her next action was barely thought through before execution, her mind running in circles. Patty parted from him for a split second, grabbing his shoulders and digging her fingers in before easily jumping up and wrapping her long legs around his waist. It was good that he was who he was because she had to use him to support her own weight in the gesture, and since it was without warning she would have probably knocked a weaker man over. She never worried about things like that with Derek, though, she never had to. As soon as she was wrapped around him she deepened the kiss again at the angle she needed, flush up against him with his face in her hands at a perfect position for her to pour herself into him.
If this was going to be her last chance to be a 'we' with him before he changed his mind, Patty was going to take it. Her heart, her anger, frustration, love, hurt, even that tiny sting of feeling lesser of a person went into that kiss, and Patty's fingertips were twisted into the back of Derek's hair by the time she parted to try and calm her pounding heartbeat. "I'm still mad." It didn't even sound like she could pretend the proper tone, her voice tiny as she tried to stick to her original plan despite the fact that she had effectively destroyed any chance she had to convince him that she was anything other than won over.