By now your baby’s development is progressing beyond her head . . . to her back. She probably wants to sit up and look around. Feel free to prop her up with pillows into a sitting position. But continue tummy time sessions and don’t be surprised if tummy time becomes “try to sit up” time or “try to crawl” time. As her gross motor skills (coordination of large muscles) develop she will try to move her whole body around. Put that together with her fine motor skills (using muscles that control smaller movements) and she will be moving, reaching for objects, and even being able to grasp them.
Encourage, encourage, encourage. Your stimulation activity is to get excited as your baby develops these skills. Clap when she gets into a tripod position during tummy time. Get excited as she attempts to sit up. Cheer as she reaches. Celebrate when she takes hold of that object!