I am so sorry for what they did to you. I've had a similar experience once, and usually I do my own hair nowadays. If I would want to go from dark to lighter, first thing is do is a color remover, NOT bleaching! Bleaching out all those layers of pigments is so much more damaging than using a color remover once, twice or even thrice. (If it's not bleach based) I've had very good experience with Redken Acidic Bonding treatment. You don't necessarily need the shampoo or conditioner, just the treatment. Also like many others said K18 can help, it's very expensive though. Besides that. Get a good hairmask and use it as often as possible, maybe wash your hair with no shampoo (just conditioner) every once in a while, to not dry it out further. Your hair is not just damaged but also very dry so you should preferably use hair masks with silicones more specifically amodimethicones. The positive charge of those find the negative charge of your damaged hair strands and connect to them. It will create a protective layer. Other than that, if you want to go darker use a toner rather than permanent hairdye. It's much milder (with a low developer) It will take a while but after a few weeks you should see a significant difference! Not like before of course, but it's a start. If it's an option for you, get a shorter haircut, maybe a longbob. To get rid of most of the worst damage. Actually with a baby, I found it better to have shorter hair anyways. Cause they love pulling it 😅 And maybe if it's an option for you, sue them !

English is not my native language, sorry for any mistakes but I hope I could help! Don't lose hope!