16 week turning on side

My baby is 15 weeks and we're transitioning her to her pack n play flat and then we're going to eventually put her in her crib flat ...last night was the first night in the Pack N Play flat and all my all she did was try to roll to her side sometime successful ...but struggled to get on her side rolling back and fourth...which caused her paci to fall out several times and her start crying...she didnt settle all night...will she eventually master the side sleeping thing? Or can this just be the 4 month sleep regression 5i keep hearing about.