Sleep on her side

Ma
I just wanted to ask if it is ok to sleep on sides. My LO is 3 months and sleeps on her side, moreover she hates sleeping on her back and does not sleep on her tummy. I don't know what to do should i place a soft pillow beneath her head to keep it elevated. Because even if we sleep on our side without a pillow that shoulder starts aching.
#First time mommy #3 month baby #Side sleeper LO