Really?

After getting Max's signal, she had started casting her new spell [ Metallic Sand Spear ] which she used only one time before during the training because of enormous mana consumption and time it takes for casting.

Therefore it wasn't possible for her to use this spell if she was fighting alone but she was not alone right now and had teammates to give her enough time to cast it. 

As the name suggests, this spell uses the tiny metal particles present in the sand to make it more powerful. 

After she was done casting it, a 3.5 meter long and one feet thick spear with black Metallic sheen materialised above her. This spell was a middle-grade, mid tier spell. Because there were very few sand elemental disciples and elder Nena found her talent promising, she has given her the privilege to choose this one tier higher spell than what was permitted.