Good negotiation skills = good communication skills. Communication is a skill that 80% of the engineers I meet don’t have. Don’t be upset that someone negotiated a higher salary than you when they were hired, you could have tried just the same.
Let’s also not discount the fact that negotiation is a skill itself, and you were learning from your stepsister who sounds like a skilled negotiator. If you had to negotiate another raise in-person I would bet you could think back to the cards and knock it out.