Gripe water. It's like magic. No need to add it to the bottles (although you can). We just give the infant dose straight from the medicine dropper and it has always worked to immediately get rid of hiccups. I think you can only do six doses per day though, so I would wait until the hiccups are really bothering her to give it.
LO's hiccups have gotten a lot better over the weeks. We are almost 12 weeks old and hardly ever get hiccups anymore. Good luck!