Lucy doesn't have a lot of stamina when it comes to magic. She struggled to summon 2 spirits before. Well, I feel good that things actually got interesting since I'm waiting on the anime to adapt Tartarus arc.
Beelzebub's anime needs a 2nd season, but I doubt it will since the manga made poor sales and the story was going nowhere. Folks said Fairy Tail was worse. Look at Beelzebub, it went down hill after Demon Pillar arc personally for me.