Hello. My girl is 10.5 weeks old and currently sleeping through the night well. She is placed in a love to dream arms up but enclosed swaddle pouch on her back and then we tuck a sheet in over the top. Last 2 days I've found her completely out of that sheet and most of the way up the bassinet. Do I persist with the sheet or is this the point I need to try arms out? If I need to do arms out do you remove the sheet?

Many babies wriggle & squirm for different reasons.
Often they will then start to escape their swaddle (if using a standard muslin swaddle/wrap.) Some can’t escape their swaddle (eg in product like you describe) & end up in various positions within the sleep environment.
For some this is the beginning of the “rolling” development stage.
Some babies like to have their hands free to touch their face &/or suck their fingers.

It is probably time to cease wrapping/swaddling
Red Nose recommends that you consider arms out from about 3 months in preparation for rolling.
https://rednose.org.au/article/safe-wrapping-or-swaddling-when-to-stop-and-how-to-select-a-safe-sleep-bag

Try removing her swaddle bag & allow arms free & see if she is more settled. If not, consider moving her to her cot in preparation for rolling.
Baby needs arms free & space of a cot to roll well.

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.
Continue to always place baby on back for sleep.
https://rednose.org.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over