Often times, girls will repeat letters to show that they are interested in them. This is evident in a text message. She isn’t trusting you because you’re not confident about your words. Texting a girl is a delicate affair. It’s better to use extra letters if it’s possible to convey your message. If she does this, you’ve failed.
The extra letters are often used to emphasize certain words and make the text more approachable. Teenage girls almost always use them, but anyone can use them in moderation. If the girl uses extra letters in a happy tone, it’s an indication that she is looking forward to speaking with you. A couple of other ways to figure out what she really feels is to ask her. You might even be able to ask her if she feels a certain way, without even realizing.