I am a us citizen and I would like to bring my 14 year old niece here to visit for about a month. Her mom will sign any papers needed to bring her here. How should I go about doing this? Is it difficult to obtain?

That all depends on what country she is from... it might be no problem at all... or a HUGE problem depending on her citizenship.

That all depends on what country she is from......it might be no problem at all...or a HUGE problem depending on her citizenship. she lives in Mexico.

That's going to be one of the more difficult ones... so get started on it, before the annual quotas are reached.. (Countries with high numbers of illegals have the hardest time and lowest quotas as a result)

Her parents should be her sponsor, not you. Otherwise, the chance to get a visa would be zero.