Is this a natural expression? Which does sound more natural, this sentence vs "I was into my modeling career for two years."? Is there any other way I can express the same meaning as this sentence?
Excellent question. This is a very natural and common way to express information about a part of a period of time. Simply put, it means the first 2 years of the entirety of her modelling career. You are in (and have covered) those 2 years out of the total. It doesn't mean 2 + total. It's like saying you're already three hours into reading a 10-hour book, so you still have seven hours to read remaining. Another way she could express this would be to say "after 2 years of modelling". If you're "into something", it means you really like it. Saying, "I was into my modelling career for two years" would mean that she really liked her modelling career for two years. Which is not what she wants to express here. Ex: Two hours into the journey I really needed the bathroom. Ex: After travelling for two hours I really needed the bathroom.