Reasons:
It wont be like some day she will even think of proposing Armaan
It will be hard but it is far better than porposing and getting rejected
In future might be possible that they will become good friends and if any guy is flirting with her, Armaan might feel insecure but won't realize its love😆
Just imagine woud'nt it have been bogus that one day she would finally express herself and he says,"kya ? par kyun... sorry but maine tumhare baare mein aisa kabhi nahi soncha."
she might have felt really embarassed... Might be later after this he might realize his love for shilpa but that would be kindaaa hard on viewers to watch till that date
Next, from now on it would'nt be like just shilpa feeling this way but instead it might just happen that she might just ignore armaan when ever he is in close proximity and he might be keen on knowing her behavior someday and there is also a possiblity that he might jump in her house to ask her and find clues like she being sister of Ridz and wonder how come no one stays with her at home.
There might a possiblity tht later one when ridz scolds her, armaan might give a crying shoulder to her ... by saying she is ur senoir blah blah blaa
When once he finally might come to know she is ridz sister that toh it would be like shilpa would be on sympathizing side and everyone would try to become her friends, especially Armaan and
If ridz would dislike liking her then surely armaan might make her realize that even she was adopted and she has no right to behave like this with shilpa and give shilpa a crying shoulder...😉
What do you guys think?