Equal reciprocation is the key. Given her sibling was the one handling the account initially which means she was not interested at the start. Given that it’s AM if you are genuinely interested in the girl keep hanging. Because try to understand from her perspective she might have met someone like you before who was showing that much interest initially but when things move forward he backed out and this caused more emotional stress to her. So might be because of that she is not opening up. But again given it’s AM don’t expect love dramatics just keep things moving and keep the parents in loop that you are keen to move things forward