What if ANYTHING she drops into a firepit brings it to max.
This could be a lovely advantage OR disadvantage. Drop 1 cut grass into a fire and BOOM, top tier fire. In addition to being useful in keeping a base's fire roaring for almost 0 cost, it flirts with the idea that she truly is compulsive when it comes to fire. A pyromaniac who just can't help herself.
Additionally, without even touching the lighter, the lighter suddenly becomes FAR more important to her repertoire, as it gives her the ability to offset her fire compulsion with her lighter's ability to cook food, so she's not screwed if she just wants to cook 1 little thing on the fire in summer and not have her whole team pissed cause she dropped a twig in the fire pit and lit the base up.