Vacillating in her answer mail that needs to be rushed

It seems like you're describing a situation where someone is hesitating or being indecisive in their response, and it's urgent that they provide a quick answer. Here's a rewritten version of your sentence:

"Her response was vacillating, and she needed to rush her answer to meet the deadline."

Or, if you'd like to rephrase it slightly:

"She was struggling to commit to an answer, and the pressure was on to deliver a swift response."

Let me know if there's anything else I can help with!