Ehhh... she showed up for me. But eh. The dinner itself isn't really locking in anything. To be honest, I wanted my fish back so I just made sure she lived and was happy with me. It didn't affect my relationship with Liara in the slightest. The stripper thing however locks it in. And I never once did that. It was too weird for me when I saw it on youtube.
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.
In ME3 you can lock in romances differently than in ME2. I couldn't go with both Liara and Traynor in ME3, for instance, cause you lock one or the other in depending on things (the shower for Traynor, the cafe and saying yes for the second time with Liara). But I could go with Liara and Kelly in ME2 because Liara decided to be the Shadow Broker. She just will probably say something if you do the Shadow Broker mission after the lock-in of the original romance.