We have established by now that the answer is ...
... an anagram of the given letters plus one additional letter. According to the OP, not all such answers are valid, though.
There is a hint in the title:
"Scrambbled" is "scrambled" plus the letter "b", but it might also be "scrabbled" plus "m".
Let's follow this hint and ...
... determine the Scrabble scores for the example answers:
These scores are not the same for all answers, but they share a common property: They are all prime numbers.
The answer is therefore:
INTERVAL with a Scrabble score of 11. (There's also "inflater" with the same score, but "interval" seems to be a more common word.)
Thanks, feelinferrety, for doing the legwork of finding the possible anagrams.