One resident said the fine rain looked like snow but she couldn't be sure because this was the first time she had seen such a phenomenon.
Is the above sentence correct?
The sentence is fine and, without your knowing it, you have balanced subordinate clauses and coordinate clauses.
Remember the acronym : FANBOYS
They go with coordinate clauses and there is a handful of them as these.
Subordinating conjunctions are many. Always read the subordinate clause along with the subordinating conjunction. You will find that they not only link but also make the clause limp (dependent). Coordinates do not; they just link meaningfully. The clauses there are self sufficient.
Sorry for the digression but it may be of help to the poster.
These are the subordinate clauses.
I find the compound sentence alright. Now you can also judge for yourself!