Her hair still looks quite thick and healthy (based off of just the photos). It could be as simple as her going through a shedding phase. Here’s some information from another thread as your question is similar to another mom’s. Take a close look at the questions that I asked her. Those may help you get to the route of her shedding/breakage:
“Well first we have to make a differentiation between whether or not it’s shedding or if she’s experiencing breakage. Shedding is natural and occurs on a daily basis. On average, a healthy head of hair sheds 150 hairs per day. You’ll know it’s shed hair because you’ll see the white bulb still attached to the end. (The part that was in the scalp.)
If her hair is breaking then we need to figure out the why before we can fix it. There could be a ton of reasons so you’ll have to really take a close look at your regimen. Are you only detangling her hair section by section when it’s damp and slick with conditioner? Do you only use your fingers and a wide-tooth comb when detangling? Are you deep conditioning her hair weekly or at least bi-weekly? Has she been swimming in chlorine a lot this summer? Does she wear a satin cap or sleep on a satin pillowcase EVERY night? Is she taking any new medications or suffered any serious stressors? (Change of school? Parent gone or deployed?) Those are just a few things that can cause breakage.
Once you’ve determined the cause, fix it then start her on a weekly deep conditioning regimen and make sure you’re sealing with a natural oil afterward.”
If you’ve pinpointed the cause and need help with how to fix it, let me know. 🙂