So if you are asking 'why does my Maidenhair keep dying', it may be getting too much sunlight, its too hot and the soil is inconsistently moist. Perhaps overfertilizing is the issue.
The Maidenhair is a thirsty species, for best results water it regularly and never allow it to dry out. The Maidenhair prefers bright indirect light, which it will get if you can provide it with the widest possible view of sky in an indirect manner. It will cope with a small amount of direct light, but ensure you are watching the soil moisture levels.
Other nuances, the Maidenhair doesn't love being repotted and will do well in a smaller pot. It likes humidity so you can either mist it regularly, or set it on a tray with pebbles full of water, so that it can harness the moisture.
To revive a Maidenhair, simply cut it back, give it a good water, some consistent attention and you will be rewarded.
The Maidenhair is non-toxic to cats and dogs.