In an Anki deck I downloaded, the Chinese translation of "Her treatment of the guests is very friendly." is given as "她对待客人很友好。" Shouldn't it be "她对待客人得很友好。"?
The first sentence is correct. You don't need a "得" in this sentence.
Here I want to show you a way to maintain your express correct and beautiful.
The key point you can check your gramma in an easy way is detecting the main branch of a sentence and then do some extensions.
The main branch of "Her treatment of the guests is very friendly." is "Her treatment is friendly.(她的招待是友好的。)".
After clarify the main branch of a sentence, you can now add the details into your sentence, it's always a best way.
The sentence now looks like:
"Her treatment of the guests is very friendly.(她对客人的 招待是 很 友好的)"
At last, change and delete some words, which makes your expression more fluent and direct.
"她对客人的 招待是 很 友好的" -> "她招待客人很友好"
Step by step, a correct and beautiful Chinese sentence is created by yourself.Is it interesting?
Hope my answer helps you.
"她对待客人很友好。" Shouldn't it be "她对待客人得很友好。"?
她 (she) = subject
对待 (treats) = verb
客人 (guests) = object
很友好 (very friendly) = adverbial phrase for the verb 对待 (treats)
"她对待客人很友好" (she treats guests very friendly) is a simple SVO sentence. I presume you can tell it is a proper sentence if you read it carefully.
I am more concern about the fact that you don't know how to use '得' as a verb particle that indicate the result or degree.
"她对待客人得很友好。" is incorrect use of the verb particle '得' to indicate the degree of the verb
The correct form is:
[1. verb] + [2. 得] + [3. adverbial phrase that indicates degree] = [1. 对待] +[2. 得] +[3. 很友好]
(it describes the degree of the verb: 'To what degree she treats guests?'-- 'To the degree of very friendly' )
In "她对待客人对待得很友好": [她对待客人] is the topic; [对待(得)很友好] is the comment
'how does she treat guests?' 'she treats guests (to the degree of) very friendly'
SVO sentence: "他(S) 吃飯(V) 很快 (adv)"
Topic + comment sentence: "他吃飯 (topic) + 吃得很快 (comment)"
break down of '吃得很快':
得 (verb particle: to the degree of)
很快(adv): very fast (adverbial phrase that describes the degree of the verb)