I'm a bit confused about this whole wali business.... I've heard that a woman needs to have one of her mahrams or a wali present when she signs the marriage contract, but who can be the wali? I've heard from some that it needs to be one of the mahrams, but how does that work for converts? None of her relatives are muslims! And how does it work if she has her parents' consent (even if they're not muslims), but they cannot be present for various reasons, and she has no appointed wali? Will the marriage be invalid??

For most reverts, the imam at their masjid acts as the imam, and chaperons any visits between the two people, gives his approval to the marriage, etc.

So sis, whichever masjid you usually go to, just tell them you would like to get married, but don't have a wali since you are a revert, and inshaAllah the imam will help you through the process.

And what if one of them was living in another country and she went there to get married? Should they talk to an imam there or?

Yup, I guess any imam could do the job, just go see one, explain your situation, and he'll tell you what to do inshaAllah.

But do not be persistant because the imam has other duties like leading prayers to fulfill so you may have to wait a bit,just be patient insh'Allah.

yh as the brothers nd sisters said ...

A Muslimah need a wali in Ijab Qobul (marriage contract). If she has no mahram who can be her wali, a non-mahram adult Muslim male can be a Wali Haqeem for her.