How old is the bird? Babies of both sexes have wing and tail markings like hens, and the boys lose the markings at maturity. Wing and tail markings on a lutino are yellow on yellow, so you need good light to see them - sunlight is best. You also need good contrast between the yellow tones - if they're about the same shade you may not be able to see the difference. If the bird is lutino pied (which is difficult to determine), it may not have any wing or tail markings regardless of age or sex.
Do you know anything about the bird's parents? If mom was NOT a lutino, this bird has to be a girl. If Mom WAS lutino, the bird could be either sex.