Hello, my 1 week old wears a cocoon sleep bag to bed and tends to elevate her legs within the bag and roll onto her side in the night. Even when I move her back to her back, she rolls back almost immediately. What should I do please?

Some babies do wriggle & squirm & can be quite active & will move or roll around the bassinet.
Some babies do not respond well to swaddling/wrapping.
Sometimes it is because they like hands free to touch their face or suck on fingers.

Still always place her on her back for sleep.
Does she always roll to the same side?
Is the sleep suit you are using like a swaddle? ie arms are not free?
Some babies like arms free & will wriggle & roll especially to side in an attempt to get arms free.
You could try sleeping her in a sleeping bag (arms free) or you could use a muslin type wrap with arms out.

Red Nose does not recommend the use of any product that “restrains” a baby in a specific position.
Have you started tummy time when awake yet? How does she go?

Have you seen your Midwife/Maternal/Child Health Nurse yet?
Did you chat with them about this?