Not small at all. Here's a link to Behira's thread: https://ball-pythons.net/forums/show...rst-BCI/page82
Behira is my 5 1/2 year old female BI. She's about 5.5-6FT and about 2.5kg. People grow them differently and she's still on medium rats (110-130G). I'll move her to Large rats soon, but right now she's also eating every two weeks, and doing great. I've seen Boas bigger and smaller at Behira's age, but I would say she's smallish-average. That's probably good for her longevity, but not great for bragging rights (many people seem to care about that for some reason - or getting them to breed quickly to their detriment).
What are you feeding Tina and how often?
I also agree with Boger - she looks more like 5+ FT to me. Behira is in a 6FT long tank and stretched out might just reach tail to nose, but I think she's a little short. I think Tina looks closer to Behira's size than you think. They are heavy bodied snakes so they can proportionally play tricks on our eyes and seem shorter than they are.
Having said all that, I think Tina looks pretty good. Remember, you want your boa(s) to have a lean/muscular squarish look. You don't want them to be rounded on the sides.
Let us know what she's eating and how often and that can help determine what to do long-term with her.