I think with photo books title isn't too important, so really "Happy 75th Birthday" is fine. I think she might get a kick out of the title "This is Your Life" which really isn't an implication her fun is in the past but a reference to an old TV show. If you want to go with a "Patty" illiteration, how about "Patty's Parties and Pastimes".
I personally love captioning the roller coaster with "its been a wild ride so far!" I think if you want to add "can't wait to see what the future brings" I personally would add another photo referencing the future - her with a baby grandchild, a postcard of a city she has a vacation planned to, etc.