'Timid and needing to show more assertiveness'
Clinical rotations are your chance to get your feet wet. You are allowed to make mistakes, not know all the answers, and voice worries or fears in a supportive environment. Therefore, its OK to be timid, but if you only have 2 weeks left then just go for it! jump in and say "let me do that!"
Also, consider this: If she has pointed this out, most probably, it is not to make you feel inadequate as a human, it is to push you to get more out of your clinicals than what she sees. The goal of all teachers is student success.
If you feel unsure then may i suggest clarify with her what specific actions you could take to overcome this. (that shows communication skills)
Worst case senaio: you jump in, attempt a task and dont excell, the CI says you need more time. thats not just for your education and success, it is for patient safety (the later is always #1 priority)
Quiet and timid are two different traits. Although most timid people are quiet, not all quiet people are necessarily timid. However, timid persons may be what we, as seasoned nurses, may call thin skinned, and that will make any work environment difficult.
School is stressful. Chances are you read her wrong, took too much to heart. I'm sure you will do fine, dont be afraid, timid or overwhelmed; take a deep breath, have faith in yourself and leap into the unknown