The correct option to fill in the blank in the given sentence is: with

The sentence would be: "Sangeeta's head is teeming with innovative ideas."

• With is the most natural and idiomatic preposition to use in this context. It suggests that Sangeeta's head is filled with innovative ideas, emphasizing the abundance and vibrancy of her imagination.
• On implies that the ideas are somehow resting or perched on top of her head, which doesn't capture the sense of teeming fullness.
• In and at doesn't fit grammatically or idiomatically in this context.