Having paid close to £100 for her ticket she was "flabbergasted" to find an "enormous metal wall" blocking a substantial portion of the playing area.
Fellow rugby fans voiced their dismay and support for Petterson on social media.
One supporter replied: "An absolute disgrace … Daylight robbery!"
Another added: "Wow I wouldn't be happy, I didn't know those kind of seats existed! I go to several games a year and never been allocated seats there!"
Many felt that the unfortunate spectator should receive some form of compensation. One fan said: "That's awful Jane. Didn't think there was a seat in the stadium like that. Certainly should be warned and discounted."
To make matters worse, Wales lost 27-23 to Six Nations table-toppers France as Les Bleus won in Cardiff for the first time in 10 years.
But there was a silver lining through the power of social media. Petterson revealed the Welsh Rugby Union contacted her after her post went viral and offered her a partial refund.
"Wow, completely mindblown at the power of twitter! Welsh Rugby Union called today," she said. "Said there'd been a 'pricing error' with my seat and they refunded me £50! Have suggested that they show the actual seat view and charge less for that seat in future. Cheers for all the support."