So now I am considering confronting her about how she essentially said I wasn't working hard enough while at the same time, essentially, admitting that the work required for her position (less than two skips and a jump from mine) is too much for her to handle.

NO. You have no idea how this person's life will interact with yours in the future. You have no idea WHO THIS PERSON WILL GOSSIP TO about you. Maybe one of her friends will be the HR manager next year that you need to get hired? Or your new boss? Or any of a million scenarios we can come up with.

Part of being an adult is learning to deal with the crap of the earth and to stop taking petty sleights seriously. Build your character so that when people talk about you, they talk about your work ethic, your honor and your honesty. As someone who has works with all of the good and bad of humanity, trust me other people know about this woman and what she is like. Don't sink to her level. Be a better person... others WILL notice.

It is hard as hell, it is unfair at times, but it works out better for you over the long term.