Medical treatment is a valid reason for B visa purposes and has long been recognized as such. An extension application is the correct course of action in this case. The application needs to be fully documented with evidence from the medical provider to include: diagnosis, prognosis, course of treatment and projected timeline for treatment. The finances involved in the medical treatment and for maintenance and support without recourse to public benefits must also be fully addressed in the application and supported with appropriate documentation.
SEE:
http://travel.state.gov/visa/laws/telegrams/telegrams_1533.html regarding the cost of medical treatment issue.
8 CFR 214.2
(b) visitors
(2) Minimum six month admissions. Any B–2 visitor who is found otherwise admissible and is issued a Form I–94, will be admitted for a minimum period of six months, regardless of whether less time is requested, provided, that any required passport is valid as specified in section 212(a)(26) of the Act.
Exceptions to the minimum six month admission may be made only in individual cases upon the specific approval of the district director for good cause.
Her situation, with sufficient medical documentation, would definitely be for "good cause" to get an extra long B-2 extension.
FROM:
http://travel.state.gov/visa/temp/types/types_1262.html#10
"Documentation Needed - When Seeking to Travel for Medical Treatment
In addition to all of the documentation requirements explained above, the following documentation is also required, for persons seeking medical treatment in the U.S.:
Persons desiring to travel to the U.S. for medical treatment should be prepared to present the following, in addition to any other documentation the consular officer may require:
Medical diagnosis from a local physician, explaining the nature of the ailment and the reason the applicant requires treatment in the United States.
Letter from a physician or medical facility in the United States, expressing a willingness to treat this specific ailment and detailing the projected length and cost of treatment (including doctors’ fees, hospitalization fees, and all medical-related expenses).
Statement of financial responsibility from the individuals or an organization that will pay for the patient’s transportation, medical and living expenses. The individuals guaranteeing payment of these expenses must provide proof of ability to do so, often in the form of bank or other statements of income/savings or certified copies of income tax returns.
Persons traveling to the U.S. for medical treatment should have a statement from a doctor or institution concerning proposed medical treatment."
*****************************
INA 212
(d) (5) (A) The Attorney General may, except as provided in subparagraph (B) or in section 214(f) , in his discretion parole into the United States temporarily under such conditions as he may prescribe only on a case-by-case basis for
urgent humanitarian reasons or significant public benefit any alien applying for admission to the United States, but
such parole of such alien shall not be regarded as an admission of the alien and when the purposes of such parole shall, in the opinion of the Attorney General, have been served the alien shall forthwith return or be returned to the custody from which he was paroled and thereafter his case shall continue to be dealt with in the same manner as that of any other applicant for admission to the United States.
Humanitarian Parole would have the strange effect of negating her prior lawful admission and she would return to the status of an "arriving alien seeking admission". That is a wierd "legal limbo status". Not really appropriate and would likely be denied in favor of an extended B-2 status.