I don’t see what is so unusual about anyone having doubts, off and on. There are periods of light and periods of darkness because we’re human and until we see Him face to face, doubts are part of the “test”.
The bible is full of examples of people who questioned or doubted God.
The letters that she left behind indicates that she had doubt half her life, not off and on with periods of lights and darkness. Whatever our emotions are at any time, we rest in God’s faithful promises, not in what we feel.
Feelings or lack of them are not evidence for or aganist faith. Worship, obedience, works of love for the sake of Christ are evidence of a faith that is stronger than any feeling.