I have seen her with actual books a few times, but she mostly reads on her Kindle. So, no.The first thing I thought is if she is so intellectually active maybe she would be pleased to take the test in first person. Or are you afraid she would not tell you the result?
That seems more feeler than thinker.
That is strange. How can you state she reads a lot without knowing the content of the books she reads? Do you see often her around the house with a book in hand? Do you see her often in the act of reading?
By the other things you said, it seems to me too she reads a lot, because it is not probable she is reading few things very very slowly. But this is only an inference not a fact.
Not only, but let us guess she has those books. Around the house? Unlikely, you could check them and know what she reads. In a closed location, like you are not allowed to enter in her room? Curious.
And, logically we can guess those books also are not available to you because they are borrowed from friends or library. So, she likes books but she does not like owning them? That's a feeler.
So you think she is INFP? You only specified that you think she is a feeler