Well, you should not have allowed her to be exposed to gambling at such a young age even though there's a chance that she might end up discovering it by herself when she's older but this is better because she would have the mental capacity to handle the pressure that comes with gambling. You can't change what has already happened but you can start guiding her so she won't make mistakes as she gets older
It's always my opinion that parents look should do everything they can to look after their children and prevent them from getting involved in any thing or activity that they are not yet qualified to participate in as children who are underaged.
Underage simply means that the child's brain or mental faculty isn't yet well developed enough to handle the who stress that goes with gambling, but in the case of the op, the deed has already been done and only thing he can do now is just (exactly as you have said) start guiding the child and talking to her always about the dangers of excessive gambling or gambling too much.
If you understand how gene works you will know that there are things that parents cannot stop in their offspring. Moreover, the father said he started gambling at a very tender age, imagine someone who started gambling at the age of 10 years and according to what he narrated he is successful in his gambling which he used to start up a business. The daughter must have also gotten the knowledge that her father is a successful gambler and grew up with the mentality that she can also become a successful gambler as well. Underage gambling is very bad and should be kicked against but what I just saw here is pure gene and it cannot be controlled so the only duty of the parents is just to advice and guide such person so that they don't go astray.