My oldest didn't need to use his finger or any other guide. My youngest did best with an index card with the corner notched out. He slid that along as he read. If he got stuck on a word, or read incorrectly, I'd slide the card back over so he could sound it out.
And, I agree with the above, I wouldn't keep pushing. Back and up and let her read what she's successful at, adding just a bit of challenge as you go along. Reading should be, for the most part, enjoyable, especially once you're reading a book. The challenge should be before that when she's learning the sounds, how to blend, how to segment, etc. Book in hand needs to be at a level she feels confident.
best wishes!