Attempting to adopt niece from Tijuana, advice needed!

Hi All, My wife and I are trying to adopt our niece from her mother in Tijuana. The mother recently suffered the death of her oldest son, and it is a priority for everybody in the family to get her remaining 3 children into capable hands. The current dilemna we face is how to best carry out this process. The mother of the children is willing to sign custody of the daughter over to us. Do we adopt in Mx or in the US? Do we need a tourist visa for the little girl? She has not yet been registered with the state, so there is no birth certificate on file. My wife is a resident-alien from Mx, I am a US-born citizen. We're trying to find the quickest way possible to legally get the child here in the states so we can begin the healing process. We are currently waiting on an email from an atty we are contacting in Mx, but we're hoping for any other information we can gleam in the meantime. Anybody have any experience/familiarity with the laws in this arena? [list] [*]Mother is willing to sign over custody [*]Adopting father is US citizen [*]Adopting mother is mexican citizen, us resident alien [*] Child has not been registered with the state yet [/list]