Step 1 (Identify the clause in question).
The clause "Although she tried her best" cannot stand alone as a complete sentence — it leaves the thought incomplete. Step 2 (Determine clause type).
Clauses that cannot stand alone and depend on a main clause to complete meaning are called dependent clauses.
A dependent clause that functions as part of the main sentence and begins with a subordinating conjunction (like "although") is specifically a subordinate clause. Step 3 (Relationship to the rest of the sentence).
Here, the main clause is "she couldn't win the competition." The subordinate clause adds contrast.
\[
{\text{Subordinate clause (Option (c)}}
\]