The Consulate will determine whether they are happy that the I 864 requirements are met.
The initial assessment seems to be automated, the belt and braces approach is to use a well qualified joint sponsor.
It is free to apply for an expedite as far as success is concerned I do not see what has really changed.
Good that she is returning to obtain treatment, the Mexico side trip just seems to have wasted time.
A local Family Lawyer would be able to advise what your State requirements are, and a Lawyer would be able to advise on all the other issues that adoption arises.