Navigating situations like this can be tricky as it's important to preserve the feelings of your coworker while also addressing the issue at hand. Here are a few diplomatic suggestions:
Subtly change the subject: Instead of focusing on the cheesecake itself, you can start a conversation about other types of desserts. For example, you could say, "I've been craving chocolate chip cookies recently, does anyone have a good recipe?" This might encourage your coworker to try baking something different.
Organize a themed potluck: Suggest a weekly or monthly themed food day where everyone brings a different type of dish. Themes could be related to different types of cuisine, specific dishes, or meals (like appetizers or salads). This way, the cheesecake might naturally be phased out.
Offer constructive feedback: If you feel comfortable doing so, you can gently give some feedback about the cheesecake. It's important to approach this with sensitivity. You might say, "The cheesecake is always a treat, but I noticed it's a little too sweet for my taste. Have you ever tried a less sweet version?"
Confide in your coworker: If your relationship with the coworker is good enough, you could approach her and gently explain the situation. Be sure to express your appreciation for her efforts and kindness before gently letting her know that while you loved the gesture, the cheesecake wasn't quite to your taste.
Remember to approach the situation with kindness and understanding. It's likely that she's bringing the cheesecake because she thinks everyone enjoys it, and her intentions are good.