Here is the full sentence. It tells about how difficult it was to look after an elderly parent, and that it has become even more difficult than it was at the beginning.
"...When she got where she couldn't tend to her toileting needs boy, I was thinking back longingly for the days when all I had to worry about was the fight to get her into a shower."
I have 2 questions with the above sentence:
1-When I looked up "think back", I checked 4 dictionaries. "Think back" seems to be used with prepositions "to/over/on", but it is used with "for" in the above sentence.
2-Is the sentence formal, grammatically correct and an idiomatic sentence? In other words, can this sentence be used in a formal environment?