My newborn rolls herself (while wrapped) into a side position while sleeping. Is this safe? Anything I can/should do to stop her (eg place small rolled towels on either side of her body in bassinet)?

Red Nose recommends always place baby on back to sleep.
Most babies do not roll intentionally till after 3 months.How old is your baby?

However, there seems to be a number of babies who roll to their side at a very early age, as you are describing.
Sometimes it is because these babies do not respond well to wrapping, & are less likely to roll when unwrapped, (ie both arms out)
It may also be helpful to wrap under arms only, using a muslin wrap, or not wrap at all, but use a sleeping bag.
https://rednose.org.au/article/wrapping-babies

Red Nose does not recommend the use of sleep positioners of any type to stop baby from rolling & has the following information.
This includes a rolled up towels.

Red Nose does not recommend positional products such as anti-roll devices and items that fasten a baby into a sleeping position.
Products that restrict the movement of a baby or a baby’s head should not be used.
This is because there are no Australian Standards for these products and case studies have shown that these products can be unsafe.