Is there anything I can do so that I can pet her
Tiamat333 listen carefully. You have to put your foot down. Conures are known for being very intelligent and bullies! They smell fear. And enjoy bossing you around if you let them. (At least mine does.) My conure is a nipper. She's is in my care because her last owners were scared of her. Now she alot nicer and more accepting of strangers. That is a huge step for Athena.
First of all, NEVER try and approach her from above her head. At least not yet. Instead approach her beak. This is how other birds greet each other.
This is going to take a lot of patience and observation on your part. What you do first is get your brother to take her out of her cage and on to a table or somewhere away from the cage.
Try to get her focus on you. When you approach her with your hand, try moving your hand in slowly toward her beak. There is a good chance that she will try to nip at you, the worse thing you can do is flinch. Hold your ground and show her that you just want to scratch her beak. When she let's you, try scratching her beak gently. She will enjoy the beak scratch and most likely want more. Every conure I've ever worked with loved this.

You might have to endure a bite or two. Show her that biting will not intimidate or scare you away. As the intelligent bird she is, she will at first be confused that you are not effected by her nipping at you.
Two things that can help greatly is:
1) offer a nice treat when and only when she lets you scratch her beak.
2)While you are getting her to warm up to you, speak softly with reassuring words. Talk to her. She may not understand your words, but see will understand the tone and sweetness of your voice. It works!
Please, let us know how your relationship progresses.
:jumping40