My little one is almost 4months old, she can flip from back to tummy, but she can't support herself when we put her in sitting position. Just a guide, bout how old does your baby manage to sit unsupported?
Usually they start sitting unsupported around 6-8 months. From about 5-6 months, you may try putting your LO in the tripod position and she may be able to balance on her own for her couple of seconds:) At the moment, just keep letting sit up with support for a few seconds each time and she’ll gradually get stronger and be able to maintain the position longer.