Beautiful snake. Im pretty new to balls, but I think she looks alright sized for a year. I wouldnt call her super small, but not huge either. How much does she weight? My girl is about 6 months and weighs about 315 grams.
As far as tank sized in concerned, I think a 75 gal is way too big for your snake. I think a 20 gal is the perfect size for your snake right now. Balls don't like a ton of space and get scared if they have to move large distances to get to their hides. In the wild, balls are victim to things lke birds and it is very risky for them to have their full bodies out in the open. When they switch hides, they like to have a part of their body in a hide through he whole transition. Your snakes size will be determined by 3 main factors: 1) good husbandry such as proper temps, humidity, clean water and home etc 2) genetics: like humans, size is largely determined by genetics 3) How much you feed her. If she has a good diet, chances are she will get bigger. But dont overfeed her either. Although obesity isnt a major threat in balls, overfeeding isnt a good thing just like people
Good luck