In Spanish, the word "paciente" is a gender-neutral term that means "patient" and can refer to both male and female individuals receiving medical care. While "pacienta" is sometimes used informally to refer specifically to a female patient, it is not widely accepted or used in standard Spanish.
In your sentence, "María es muy _____," the use of "paciente" would be appropriate because it conveys that María is a patient without needing to specify gender. Therefore, "María es muy paciente" means "Maria is very patient," emphasizing her demeanor or attitude rather than her status as a patient.
If you meant to refer specifically to María as a patient in a medical context, you could say "María es muy paciente" to imply she is showing patience. In summary, "paciente" is preferred due to its gender neutrality and conventional use.