What should I say to her regarding this?

So my bd has another daughter that is a year and a half older than my nb baby . He was denying knowing if she was his but now since his mom is around there is no denying. His mom brings up the other baby often and sometimes her mom so yesterday I asked her if the bm knows he had another baby. She said I don’t know ask him if he told her… which tells me she only talks to me abt them but not the other way around which I find weird maybe cus I already know .. Not sure.