Another Not-Really-A-Spoiler Tidbit About Kelly
Yup, she can feed your fish for you. It actually provides this rather amusing line in the wikia:
If you're not interested in Kelly, it is well worth putting enough effort in to get to this stage of the friend/relationship, due to the fish services she offers. And also...Shepard can flirt with Kelly anytime prior to the suicide mission, which eventually results in a private dinner at the Captain's Cabin, after which she offers to feed Shepard's fish. It is still possible to pursue a relationship with a squadmate after this point if Shepard is solely interested in having her feed Shepard's fish.
Kelly can appear in ME: 3 as well, but it is conditional, dependant on whether or not you managed to have that dinner. If you did, she'll appear in ME: 3. If you did not have dinner with her (like what happened with my first Fem!Shep playthrough) she does not appear in the third game.
So basically, have that dinner. It doesn't have to go anywhere after that, and you gain slightly more narrative in the third game. And fish feeding services. All about that fish, really.