However, there are a few things to note:
* Clarity: It is often better to be more specific about what "better" means. For example:
* "She was feeling much better than yesterday."
* "Her health was much better than yesterday."
* "She performed much better than yesterday."
* Comparison: The sentence compares her state to a previous day. If you want to compare her to someone else, you'd need to adjust the sentence:
* "She was much better than *him* yesterday."
Overall, the original sentence is grammatically correct, but adding more context can make it clearer and more impactful.