The most common and most likely answer to this crossword clue is the 1 plus 3 plus 2 plus 4 plus 6 letter word A BEE IN ONES BONNET
I've seen this crossword clue in The Times
A
B
E
E
I
N
O
N
E
S
B
O
N
N
E
T
Buddy explains!
The straight part
We know that "Thing troubling babe, soon nineteen" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case thing troubling babe, soon nineteen = a bee in ones bonnet.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.