My 6 week old is always placed on her back to sleep in her bassinet but has recently started rolling onto her side in her sleep. She is able to roll herself onto her back again and has never rolled onto her front. Is this something I need to be stopping her from doing re SIDS risk? I don’t know how I’d be able to stay up all night watching her. Thanks!

Most babies will be rolling over by 4- 5 months. Some earlier, some later.
This is very normal as babies grow & become stronger.
Many babies then prefer to sleep on their side or tummy.
This is not something that needs to be stopped. It is important to make her new environment as safe as possible.
https://rednose.org.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over

How does she go with tummy time when awake?
Increase her tummy time when awake - more frequently if she is not tolerating long periods on her tummy.
Increased tummy time when awake helps to build upper body strength to assist with rolling both ways.

Some babies like to touch their face &/or suck on their fingers - if these babies are swaddled with arms in, they will often wriggle in an attempt to get arms free.
In this case we would suggest you have her arms free (also because she is rolling.)
You may also want to move her from bassinet to cot if she continues to roll. (see info linked above)

Continue to always place her on her back for sleep.

Have you tried to gently roll her back? What happens if you do?
Babies need arms free & the space of a cot to roll well.
You are correct Parents are not expected to sit up all night observing baby. This is not achievable.in the long term.