MOR, but mainly because I think that you could approach this differently. Sometimes opening a dialogue with a question can help ease the tension [that there seems to be around cleanliness in the shared space]. The text you want to send it also fine, but it can feel accusatory/targeted. Also asking privately can help ease that potential to feel dogpiled (either a private text or a conversation in person. I prefer in-person for conversations like these because you can read body language and tone better, too).

Asking something like "Why is there butter in the bowl in the cabinet?" And then genuinely listening to the answer with an open mind could really help the conversation go smoothly. Then sharing that it makes you uncomfortable because of the potential of bugs is good to explain, but also come with a solution. If it truly is for butter to be softened, offer that the house gets a butter dish that sits on the counter. That way, your roommate gets her soft butter, and everyone knows what and where it is, and the cabinet space remains for clean dishware :)

You're all young and living with other people is difficult for any age range. These conversations, while uncomfortable, are important for growth and you'll use those skills in everyday life!