My 3 month old isn't responding to any visual cues. she has an absent septum pellucidum. should i worry that she is blind?

Concerning: Absence of the septum pellucidum is associated with optic nerve hypoplasia and developmental delays. Do the eyes shake (nystagmus)? Some crossing of the eyes is normal at this age, but constant deviation is not. Go see a pediatric ophthalmologist for an evaluation.

Visual clues: Yes there us a good chance that she is blind because her optic discs may be missing.

Yes: Please take her to a pediatric ophthalmologist for evaluation.