Catch up with the first installment looking at "Kuroko Shirai"
Catch up with the second installment looking at "Accelerator"
She is a member of ITEM, a mercenary group in the dark side of Academy City that Misaka encounters. Due to AIM Stalker, Rikou is a vital member of ITEM and a dangerous enemy to have breathing.
Although AIM Stalker isn't a dangerous ability itself, coupled with the fact that people need to eat and sleep, Rikou just needs to point others in the right direction while sitting back and waiting for her enemies to be killed. According to her, her power is so strong and accurate that she can track someone even if they leave the freaking solar system. A living GPS ladies and gentlemen.
Physically, she isn't powerful and in a one-on-one fight, Rikou would most likely lose to anyone stronger than herself. I'm sure even a Level-1 could take her down. Unfortunately ITEM works as a team and there are other ways to defeat someone other than beating them in a fist fight.
Knowing the location of your target at all times is a tremendous advantage considering it's more or less the same as seeing through walls. Put a gun or any other projectile weapon in Rikou's hands and it's more or less game over.