In this situation, the best response would be:
Work with the guest to find another day to schedule the Spa services.
While it can be tempting to offer a quick workaround, such as squeezing the guest into treatment rooms or offering a different package, it's important to prioritize the guest's overall experience. Apologizing sincerely for the mix-up and showing empathy for her disappointment is crucial. By offering to schedule her for another day, you can ensure she receives the full Spa experience her husband intended for her, which is ultimately more valuable than a rushed alternative. You might also consider offering a complimentary upgrade or bonus service for her next visit to show goodwill and make amends for the inconvenience.