Hi, I currently have a very active and “refluxy” 9 week old that still has her startle reflex and has not shown signs of rolling in play. She currently sleeps in a bedside bassinet and uses love to dream swaddle sacks and an ergo baby tuck sheet to sleep. In sleep she started using her stomach muscles to wiggle herself up out of the tuck sheet and uses her muscles to throw her weight around rotating to her side. I am apprehensive to call this rolling as she uses the bottom half of her body not her top half. I always put her down on her back but two nights ago I woke to her untucked on top of the ergo baby tuck sheet and on her side. Do I continue to tuck her? Do I start to transition her out of a swaddle sleep sack even though her reflexes are really strong and she hasn’t shown signs of rolling in play?

Some babies do not respond well to swaddling as they like to be able to touch their face &/or suck on their fingers.
In an effort to do this they wriggle & squirm & sometimes end up accidentally rolling over to their side.  or tummy &/or kick off bedding.(or escape tuck sheets.)
It can help to no longer swaddle baby with arms in or else stop altogether.
It may help to use a sleeping bag with arms out, in place of the swaddle suit/sack.
Still always place her on her back for sleep.

How does she go with tummy time when awake?

She may be close to rolling, also.
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 the “new” environment as safe as possible.
https://rednose.org.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over

If she does start to roll soon, she will also need to be transferred to cot from bassinet.
Ensure mattress is firm, well-fitting & flat (not elevated in any way)
Always place baby on back for sleep.