Hi
Since nobody else answered here's a few thoughts. Not sure about your climate. Dicksonia is the most cold tolerant of the treeferns but does require high humidity like all the others. Lots of water and at least semmi shady. I have trouble with browning fronds during winter but I think more related to low humidity than temps.
If it was growing outside, obviously, enough climate was provided to support it.
Wish I could be of more help but i know nothing about temperate climates. gary

Do you know how to water it? The ENTIRE trunk needs to be completely soaked every day during the summer - start from the crown and work down. Don't waste effort watering the ground, as it's only by paying attention to the trunk that you stand any chance at all of saving this neglected and now almost terminal tree fern. It does sounds very far gone from, what you say.