6 month old milestones?

Calm down! She's doing loads of things most 6 month olds can't, such as standing unaided for a bit- there is no reason to push the sitting thing, she's obviously developing completely normally and will sit in her own time. Just allow her opportunities to practise her sitting and she'll get there. She's not behind though, a lot of babies can't sit unaided until 7-8 months.