Translation:She went to sleep at 9:45 last night.
In Chinese, "睡觉" means exclusively "to sleep", but in English is preferred to say "to go to bed instead" although "to sleep" is perfectly usable but uncommon; for instance, it is preferred to say "I went to bet" than "I slept" as the first comment of this forum and its replies suggest.
Absolutely. It's pretty poor form by Duolingo. They should go through and check all the sentences that could have this error.
And quite a few types of errors, actually. They keep very slowly fixing them one by one. They need to get on the front foot and proactively fix them.