As long as a glass enclosure has ventilation in another place other than the top (like an Exo Terra, or Zoo med glass enclosure) they are more than fine, and in fact probably better than an all screen enclosure. Unfortunately, yours is undersized. Just because she is small, that does not mean she needs a smaller cage. I would bet her issues are stemming from improper lighting and supplementation. You should also look into bioactive substrate, this will negate your mildew/mold issue, will allow you to mist properly, and is overall a whole lot easier to maintain.