To be fair you didn't say you had.

And if push comes to shove, you can always go around her and tell your dad what she has in mind. It may be underhanded, but yes, getting a family pet is a family decision, and it will be better for everyone, including the dog, if the entire family is involved.
Go travel around the world and just enjoy.
Keep my richness a secret if possible, maybe a new identity.
Live a comfortable but not excessive lifestyle. Own the money and not the other way around.
Figure out how best to help the world with the remainder. Put money into research for alternativ energy sources, and better agriculture techniques and devices to cut down on that whole environmental footprint, or maybe become a patron for the science fiction and fantasy writers I like.
Or use my money to help finance campaignes of candidates who might actually give a [censored] about its people instead of whose funding their campaigne.
Somehow buy all the media corporations and have everyone fired and then shut them down. How you like reporting on your own job loss [censored]? Oh wait you can't report anymore......hehe...
Oh wait only a half a billion dollars........nvm
I'll just stick to travel and the agriculture stuff.