CURLY HAIR HELPP!! Little sister’s curls are gone :(

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Curly loves I need help! My little sister got her hair cut and blown out about 2 months ago, which was her first time getting it done at a salon ever! Prior to that, we only straightened her hair at home once. Other than that, I care for her hair as we have the same curl pattern, she also LOVES her curls. After this trip to the salon, her hair had a bad odor for weeks and went from this:

To this:

I’ve tried deep conditioner & finger curling, and while the curls look like they’re starting to come back when they’re wet, once they dry, they dry like the picture above. It breaks my heart, as she tells me how much she regrets going to the salon. She’s only 6 and is so insecure about her hair now. Any advice or recommended treatments? I’ve heard about Olaplex and have thought about purchasing that, but I have never had this damage before so I’m a little lost on what to do, please help😭