The teacher is asking to write a background paragraph and cant be biased but needs to use evidence. Wouldnt the evidence shows my bias if I put it in?

Nope!

Explanation:

As long as you have non-bias evidence it will not. If you wanted, you could also include evidence from "both sides" too.

Cassie was adventurous, and ambitious. She had dreams to be a brilliant scientist. She has a big sister and a little brother. Her sister was considered charming, but conceited. Her sister gets annoyed at the littlest things. While Cassie was carefree, calm, considerate, her sister was cautious and bossy. Her brother Alex was creative, brave, and cooperative. Even though they were different they loved each other and always put family first.

Idk but hope that helps