She should know when you SHOW that you do love her. The stars and that pseudoscience astrology has nothing to do with love, love comes from YOU not the stars. You might want to work on feelings before you lose her!
Cancerian women love sincerity and confidence in men. Just be sincere to her but you shouldn't look desperate, nor should you have the reverse attitude of giving her the sense that you could date any other girl. She will feel like the millionth woman on your list of occupations. Cancerian women also enjoy having some fun so take advantage of this opportunity.
Ok im smooth with girls cos i am one!! All you have to do is make a lovely photo frame out of wood that says get well soon and i love you soooo much!! then boo yah she'll know you love her! Make all the love come from your heart!!
I've got news for you, zodiac symbols do not control our feelings. Sounds like a trust issue which either you've caused or it's instilled in her from some early life problems. Actions do speak louder than words. Why does she doubt you? If you answer that maybe you'll know why she can't believe you.