The "Behind Her Blue Flame" with Selvaria are definitely worth the purchase. You get to play 3 new missions using Selvaria and you also get to learn a little more about her story. In the last mission you get to play as Selvaria in her Valkyria form and pretty much annihilate everything. I enjoyed those missions a lot.
The other map with Edy may or may not be worth it to you. It's only one mission where you play as a small detachment from Squad 7 being led by Edy. The battle was a little challenging since you are forced to use certain characters from Squad 7 but it's pretty short compared to the Selvaria missions.