My 4.5 month old keeps hitting her head on the cot edges as she moves A LOT in her sleep :( are there an bumpers or things you recommend we use to help her so she isn’t hurting herself so often?

Rolling into the sides of the cot is not unusual, especially as baby begins rolling & moving about independently.
Many babies do hit their heads or get arms/legs stuck between the slats of the cot.
Does she wake up when she hits her head?

United States Consumer Product Safety Commission data has shown that infants suffer essentially no long term injuries from contact with cot slats.

Red Nose does not recommend using soft & padded bumpers in the cot.
This is especially important as babies learn to roll. Soft padded objects in the cot can increase the risk of suffocation.
https://rednose.com.au/article/at-what-age-can-i-introduce-cot-bumpers-and-pillows