What was the name of woman who tied to train tracks on The Rocky and Bullwinkle Show?

The character you're thinking of is "Nell", also known as "The Beautiful but Dumb Blonde". She was a recurring character on The Rocky and Bullwinkle Show.

While she wasn't always tied to the tracks, she was known for her absentmindedness and often found herself in precarious situations, including being tied to the train tracks at least once.