Lae’zel does not have infravision. If fighting in the dark without a light source, she will have problems. Could this be the cause?
I assume you mean darkvision? If so then yes, fighting in areas that don't have light with characters that don't have darkvision will impose disadvantage on all attack rolls even if you are standing right next to the enemy you are trying to hit. I keep forgetting the Githyanki don't have have darkvision as it is a fairly common trait among most non-human races.
