User blog comment:FairyRaven/Fairy Tail Chapter 360:The White Inheritance, Review and Commentary/@comment-24066070-20131115194948/@comment-24066070-20131115210655

I don't know how much Gemini's functionality relies on Lucy's magical power. Besides, it's not clear how Jackal's magic works either. Is it enough to touch someone in order to turn them into a bomb? Will it fail if the opponent is too strong compared to Jackal?

If it is enough to merely touch the opponent, like some absolute magic, then Lucy will be able to do even if she has less magic power than Jackal. Furthermore we don't know how strong Gemini is, after all Spirits like Aquarius and Loke posses powerful magic on their own. Perhaps Gemini has a fairly high amount of magical power as well.

In your own review you mentioned Lucy could send her Spirits back and forth to the CSW to protect/heal them. However, it has already been mentioned several times that she gets tired when she has to keep summoning them. I think it would be less tiring for her to have Gemini perform some sort of kamikaze attack instead.

Come to think of it, a Lucy - Wendy combo may be effective as Wendy can heal fatigue, thereby allowing Lucy to summon more Spirits for longer periods of time. Though they would probably need to train together for a while before they can effectively use it against an opponent like Jackal.