I’ll do my best to explain this weird English construction:
The proper construction is “she had better” or “she’d better” instead of “she better” in formal contexts. However, “she better” is a perfectly acceptable informal American construction, derived from mishearing the contracted form. The reason is that “had” is the auxiliary verb and “better” is the adverb. When omitting “had”, “better” has to turn into the auxiliary verb, which is not usually the role of “better” in a sentence.
To be honest “she had better” is a rather odd construction in its own right, so “she better” is not going to draw the ire of most American grammarians. In spoken English, “she better” and “she’d better” are almost indistinguishable, so this is really only a written English issue.
The purpose of the construction is to provide advice in a specific instance. Sometimes people say “she’d best”, but that suggests slightly broader, vaguer advice than “she’d better”, which alludes to a specific choice. “I recommend” is for advice that is of a less consequential nature. For more general advice, the construction to use is “It is better to be” or “It would be best to”. If you’re expressing opinion rather than advice, say “I’d prefer her to” or “I’d rather she would” instead of “she’d better”. If talking about requirements rather than choices, say “she must” or “she has to” instead of “she’d better”.
To summarize: Kristen was within her right as an American writing in an informal context to say “she better” when advising Brooke on which question to answer. However, since there are Canadians and formal English writers involved with this Not-Forum, the rather polite thing to do is to write “she’d better”.
