Use indirect ways to tell her. Emails, cards, gifts, good
compliments, etc. All these are very good and indirect ways to let
her know that you are interested in her. If she is also
reciprocating, she would show you some actions likewise, else, it
is always one way from you.
Well, this is the way some guys indirectly let me know that they
are interested in me. When i just behave numb or normal, they soon
realise the meaning and back off easily without facing a direct
harsh rejection.
Love has to be mutual.