I can offer some general advice.
If your best friend asked you such a question, it's likely that they are feeling vulnerable or seeking clarification about the nature of your relationship. Whether or not she needs to respond immediately depends on the context and her current feelings. Here are a few things to consider:
Emotional State: If your friend seems distressed or upset, it may be important to respond sooner rather than later to address her concerns and provide reassurance.
Complexity of Emotions: Questions about the nature of a relationship can be complicated and may require time to process and articulate. If she seems emotionally overwhelmed, she might appreciate some time to think before responding.
Open Communication: It's essential to maintain open and honest communication. If you need some time to reflect on your feelings and thoughts about your friendship, you can let her know that you want to provide a thoughtful response and not rush into it.
Avoiding Misunderstandings: Leaving questions unanswered for too long can lead to misunderstandings and further confusion. If you can, try to respond within a reasonable timeframe to keep the lines of communication open.
Mutual Respect: Both of you should respect each other's emotions and boundaries. If she needs time to process her feelings or thoughts, allow her that space.
In summary, while there might not be an absolute need to respond immediately, it's considerate to acknowledge her message and communicate your intentions about when you can provide a thoughtful response. Every situation is unique, so consider the dynamics of your relationship and her emotional state to determine the best course of action.