Sorry if this has already been discussed here.

It seems almost certain now that the Emily McMullin who registered the trump-email.com is not Evan McMullin sister.

https://boards.4chan.org/pol/thread/115434588/mcmuffin-strikes-again#p115437697

Here is what the 4chan user have to say about it:

This is the Los Angeles, CA Emily McMullin who is his sister https://www.instagram.com/emmcmullin/ Evan is following her on Instagram and this is her twitter where she uses the same pic: https://twitter.com/EmmyMcMullin

This is the Cendyn / Boca Raton, FL Emily McMullin (my image): https://www.linkedin.com/in/emily-mcmullin-22309095

Another image of the Cendyn Emily McMullin is in this page: http://www.bocabacchanal.com/press_room/pr_WinefestAndAuction.asp

My conclusion: different people.