Hi there , My baby has hip dysplasia and on a rhino brace for 2 months now . She is now 6-month old and starting to prefer turning on the side to sleep despite awkwardness of the leg position. Is there any advice for safe sleeping for babies in brace ? Many thanks

It is quite normal for babies to be rolling by 6 months of age, & most of these babies will prefer to sleep on their side or tummy.
Red Nose recommends that babies are still placed on their backs for sleep but allow them to find their own position of comfort.
https://rednose.org.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over

While I have no specific information in relation to side sleeping for your daughter, it is normal for babies to roll & prefer to sleep on their side (& tummy) by 5-6 months of age.
If you are seeing her lifting (& holding) her head, turning & manoeuvring in the brace while awake, I see no reason why she cannot be left on her side when she gets there herself.
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Always place baby on the back for sleep.
Also check with your Health Professional if you are concerned about her sleeping position with the brace on.

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