I don't understand your motivation for telling her and your reaction afterwards. Surely if you wanted her to know for her sake you have fulfilled that objective?!
How she responds how he responds is really nothing to do with you. Making assumptions she is being gaslit and even if she is- again it's none of your business! Your actions hurt her just as much as his- and yes for the majority of the time you didn't know. But you still bare responsibility. This is where you draw a line you told her, it's down to her how she acts next.
As for your motivation, if you fear as much as you say you do him going for rights- why on earth did you rock the boat?! Surely it's not in your best interests to antagonise when you want him out of your life.
So I can only assume motivation was one or not reason- money and revenge. Revenge for how you have been treated and probably more so to gain access to maintenance. Now she knows he can pay without having to hide it. It's easier to pay. So if that was your motivation surely you now need to go to the relevant authorities in your country to sort it.
As for rights, if it's anything like here he's not done anything to harm your child so the chances are he will get visitation. Here you can get a child arrangement order to stipulate how often and holidays etc.
Clearly the money means more than visitation as you wouldn't have rocked the boat otherwise.
People can give you better advice if you are more honest about your motives, your reasoning simply doesn't add up.
Why do you care so much about how she responds??
Why did you do it??
Why are you assuming he is gas lighting- even if he is why do you care so much??
Why do this and risk him claiming rights??
It all stems back to maintenance which you are entitled too so rather than this crazy crusade of she's got to know why didn't you simply apply for it??