When is baby's neck strong enough so she can lift her head without support?

By around 4 months old, a baby should be able to hold up his/her head when being placed in a sitting position. At around 6 months of age, he/she should be able to hold his/her head steady and have rather good head control. Still, every baby develops at different rates. Speak to your doctor if your baby seems to have difficulty lifting up his/her head slightly at 3 months. You could refer to this article for more information: http://www.babycenter.com/0_baby-milestones-head-control_6579.bc By the way, your girl has very pretty eyes!!

My daughter is 7 months old and I see like she can not hold for more then 10-15 seconds at once. her head will dip for 2 second or so before coming back up. But I did felt like her neck is strong enough after 6 months.

What a cutie pie! Normally around 3 to 4 months baby will be able to raise up their head and neck. Do practise tummy time daily with him so he can develop stronger neck.