Thanks for the update. Sounds like you're feeling encouraged and more positive
If it is a lactose intolerance then that's much more simple than a protein intolerance or allergy. I haven't used it yet, but a probiotic for bubs will help with her digestive flora... Which will help her digest lactose (for when she does get it again). I haven't used it yet but one was recommended to me called 'baby biotic'. You can just put it in her bottles.
Also, I don't want to be negative but I just wanted to suggest that you take pleasure in subtle improvements and developments. As my ds was a poor sleeper from VERY early on, I was constantly looking for "it"... you know, the thing that would turn him into a textbook baby well I have never found "it", and I don't believe there is one anymore. Your dd has developed all sorts of behavioural associations with sleep because of her rocky start (like my little man) so don't be discouraged if sleep improvements are gradual and sometimes appear to be going backwards. Also, she might have a wakeful temperament and enjoy being very alert (my son!) She will become more settled, and hey, perhaps something will just click and she'll be a champion sleeper, but I guess I'm just saying to be open to the possibility that it might not happen like that so that you don't have to get yet another big kick to the guts if it's not that straightforward.
Hugs... I mean cuddles to you. I hope these changes are a real turning point for you and your family