"She had an enormous debt."
Translation:Elle avait une dette énorme.
There is not enough context to determine if it is my opinion (before the noun) or a hard fact (after the noun), hence the alternative placement.
The same would apply to "immense".
Yes because in French you normally put the adjective after the noun. But you can put before the noun the adjectives that are related to the personnal interpretation of the speaker. So in this case "enormous debt" can either be objective ("dette énorme") or subjective ("énorme dette").
A red car = une voiture rouge (it can only be objective) Un homme grand = A tall man (objective) Un grand homme = A great man (subjective)
I hope I'm clear enough