Hello, My 2.5 week old rolls from her back to her side when we attempt to pop her in the bassinet, how can we prevent this? I’ve read that sleep positioners and nests aren’t recommended.

Most babies do not roll to tummy intentionally before 3 months; however, some babies do roll, especially to the side, at a very early age.

Some babies do not respond well to wrapping/swaddling & prefer to have their arms free.         
Some babies like to touch their face or suck fingers when settling.
You could try settling him without any swaddle, or wrap with his arms out. (as for 3 mth old)
https://rednose.org.au/article/wrapping-babies

Are you using blankets? Ensure head & face remain uncovered.
She may be more settled in a cot rather than a bassinet.

Have you commenced tummy time yet when awake?
https://rednose.org.au/article/tummy-time-is-good-for-baby-because

Always place baby on the back for sleep.

You are not expected to wake during the night to keep checking on her.
However, there is nothing wrong with rolling her back if you see her on her side.

Red Nose does not recommend the use of sleep positioners.
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.
https://rednose.org.au/article/is-it-safe-to-use-products-designed-to-keep-baby-in-a-particular-position

Pods/nests are also not recommended, as many are soft & padded & may create a risk of suffocation, especially if baby is rolling.
https://rednose.org.au/article/firm-and-flat-is-safest-for-sleeping
https://rednose.org.au/article/why-is-sleeping-babies-on-firm-surfaces-so-important-and-what-are-the-risks-if-you-dont