Shelichos- What about Keddushin?

In the latest episode of Rabbi Feigenbaum's Awesome Shiur of Shiur Awesomeness, we are discussing how we know we can use a messenger, or Sheliach, for Keddushin. Originally we learned it straight from a Pasuk in Devarim, but the Gemara points out that the Pasuk in particular was discussing Gerushin, or divorces. We then learned that you can't learn Keddushin straight out from Gerushin, because Gerushin is Ba'al Korcha, against her will, and Keddushin needs her consent. From here on out, we applied Gerushin and tried to learn other Mitzvos with Shelichos, like Teruma and Korban Pesach, with Gerushin. However, I remember asking, "What about Keddushin? We learned it technically was different from Gerushin, so why can't we try to apply that to learn other Mitzvos can use Shelichos?" Truth is, we answered my question, I just flat out forgot it. So, what do you say champs? Do you have an answer to my question? Sound off on the comments below...