Is this normal? (Infant posture)

My six week old has always favored the right side and turned her head to face it. I have noticed a flat spot on her head and have been trying to do more tummy time to improve the muscle tone in her neck. Today she was with another baby for the first time and I noticed that it's not just her neck, but it appears that her whole body is tilted/curved. With more thought, I realized she has never really laid flat on the back of her head or straight up and down without assistance, including in the car seat, her baby bathtub, her basinet, etc. Here are a couple pics to illustrate. She is in the white onesie next to her friend in pink who appears to be much straighter.