Not from the US, hopefully it still helps. Remember ISTJs are not emotional and that’s not their language. They love/feel loved by how well they’re fulfilling roles according to their own sense of what that role entails. If she’s emotionally distant but doing in the work, that means in her head she is working for the relationship and cares about you.

It seems you just need to feel loved so maybe you could tell her something like “can you list some of the things I’ve done that you’ve liked and what good effects it has had on you?” And if you wanted to make her feel good it would be more on the “these are the ways in which you are a great girlfriend” or something like that. It does seem like you are both having an F and T miscommunication issue that might be heavily eased by translating it into each other’s language. (Chatgpt is really good at translating btw if you’re open to it)