Henna to Loosen Curl

I was doing a little looking online for a natural product that would help loosen curls. My daughter has 3c/4 type hair and would love to wear her hair down and curly. She has a ton of shrinkage. I came across a product from Baka called, I think, Natural Laxer mix. While researching that I found out some people have.used Henna to loosen curls. If anyone has used Henna, could you please explain the process, how much Henna, is anything mixed with the Henna, how long to leave on etc.

Also if anyone has used the baka product, how did the that work?

Any before and after pics of either process would be greatly appreciated.

Thank you so much for all the help!