How to get housemates to clean up in kitchen?

I'm a college student doing a summer internship and I'm sharing an apartment with the other interns. This is my first time living in a shared apartment, so I'm not used to these kinds of issues. It's a little early to tell if this is going to be a habit, but one of my housemates sometimes leaves dishes in the sink for a very long period of time (not just plates and eating stuff, but unwashed cookware). This time it's going on 24 hours - the dishes she used to make her dinner last night are still sitting in the sink, and they're starting to smell. She left stuff in both sinks which makes it hard for other people to use them. I don't think it's fair for anyone to have to clean up after her, and the rest of us don't have an issue cleaning our dishes right away, or at least right after we're done eating whatever we've just made. But I'm really terrible at confrontation and I'm not sure how to approach it. It feels really mom-like to say we should all agree to clean up as soon as we're done, but if that isn't already assumed (and I don't see how it wouldn't be but whatever) then I'm not sure how else to approach it. I'm sure a lot of people out there have dealt with this sort of thing before. Any ideas on how to bring it up nicely? I don't want to create animosity so early in the summer, but I also want a clean kitchen, or semi-clean at least.