Gabriel couldn't get close to the Headless Mage. And the distance between the two was so high that even if he attacked, he believed the Headless Mage could avoid it. The chances of success were low.
He didn't feel like it was the right decision to waste more strength on a half chance as he needed to reserve some strength for the next few floors as well, including her main attacks, since they were going to be more difficult than this.
At this stage, he didn't want to waste strength if he wasn't sure that it was going to help him. The Spirit Explosion also wasn't as useful in this situation since the Headless Horse wasn't getting close to him.
He needed help, and who better to help him than the person that was able to hold all the Head Council Teachers at bay?
