Can we prescribe singulair (montelukast) for girl who has asa allergy?

Yes: They are not in the same family of medications, but i can see why maybe you are asking: both singulair (montelukast) and Aspirin interfere with the arachidonic acid pathway (the one that generates different inflammatory molecules). If true allergy to aspirin, no worries because they are totally different. If pseudoallergy to asa (google it), no prob because singulair (montelukast) doesn't work like asa.