Honestly, when I think about why Imlie does not thank Aryan for all the things that he has done for her, I think it is because of one of two things, or both.
1) She really considers him her own person and knows he will always stand for her no matter what. Almost like a soulmate like connection where there is no need of words but when they display their raw/venerable emotions to the other, it helps us (the audience) understand the developmental stages these two characters are going through. She has already named her whole life to him two times now so there is no way that she doesn't have gratitude to him. I think that is the key there; when we are thankful to someone, we are "pleased and relieved" (as the dictionary describes it), but these are feelings that would eventually fade. In the other hand, gratitude is what Imlie has for Aryan, even though it is still at it's beginning stages. She never thanks him for what he has done but does everything else (cares for him, makes him food....) and enjoys doing so. That small cute smile she had when Aryan and Arpita came in in yesterdays episode definitely showed how happy she was to see him even before she started to tease him and laugh her ass off.
The second reason may be that even though Aryan did clarify to her previously, Imlie still has her doubts that Aryan may eventually use her against Aditya. She knows Aryan always thinks 10 steps ahead so she is never sure what he could do next. Even though Imlie may not like Aditya, there is no doubt that if that man is destroyed (for whatever reason Aryan may have), the direct impact would be on her "family" which she would not be able to tolerate. On one side will be the man who stands up for her, has become her sword and shield whenever needed and taught her how to face reality when nothing made sense. On the other side will be her love for the people she considers family, who has been with her for the past year and have made a room in her heart. If everything goes down badly, we all know which side she would eventually choose because it is easier to break a relationship that has no name than to one that does (even though it is at face value).
However, if that does happen, the repercussions for Imlie will be much more drastic than what she felt when she left the T house. She wont realize the extent of what she lost until she loses it because that bond and attachment she has with Aryan is not evident to her as it is with her relationship with the T.