You can file an extension if that makes the process easier but you don't have to.
If you are making the election to file a joint return, she does not have to be physically present to apply for the ITIN, but she will need to sign the W-7, so you will need to mail it to her, then have her mail it back so your can mail it to the IRS (or take it to her if you visit her first).
Because this is somewhat complicated, you can file an extension request and wait to file your return with the W-7 until she arrives in the US.
