Just text I love you and I really care about you. Write a condensed version of what you feel for your friend in words as a text. However, it is more believable if you show her your love and care in person and not in text messages.
When you talk to someone face to face, it's harder to hide deceit ... Not impossible .. just harder. When texting someone, or emailing or any other means of communication that doesn't involve a personal one on one connect it's much easier to say things aren't really REAL, not to mention deceitful and shallow.
To love and care for someone is a personal experience .. texting, however is impersonal. It's ok if you just want to remind your sweetie or if you want to relay your message using an impersonal means .. knock yourself out. You get what you pay for.