I agree, though as a longtime mystery fan, I do love a dying clue, and this had a pretty good one. But beyond Abigail's revenge murder being cruel, she imposed on and manipulated the people around her rather horribly. Rather than a sweet old lady, Abigail could have been seen as somewhat of a sociopath who knew how to press the right emotional buttons.
1) It was her safe, so you can assume she made sure it was free of all pens & pencils. She also broke the lightbulb to make it harder for him to do anything else, like write a message with bits of paper.
She didn't count on him having matches or realize their usefulness.
2) She tested whether he had anything to write with by giving him paper and demanding that he write down the combination. He didn't have anything so she gave him a pencil and then quickly and deliberately took it back.