My sister went through this w/her son in first grade. He had trouble with the letters: s, t and f. She took him after school to a speech therapist for a while and today, he's a senior and doesn't have any more problems with those letters. Apparently the therapist told her that her son used the pacifier too long and he didn't utilize his tongue properly in forming those letters.
Long story short, you might find some helpful suggestions on the net about how to work with her when sounding her letters.
Just my two cents.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
