No, it is positive. It is an affirmation that she has a good life now.
Her life is better than before. In fact, "life had never been better." That means there is no time in her previous life than was better than her life now. That means she is having the best life now.
"Never" has a negative sound to it, but it doesn't necessarily have a negative meaning (in the sense of sadness). It depends on how it is used. We can use "never" to talk about good things. For example, "I have never dropped my car keys down a storm drain," or "I have never gotten poison ivy." We could thank a host by saying "What a wonderful party! I've never had more fun!"