A shrinking violet is a very shy person, so the context is saying that she was the opposite of shy.
Context: "A bit of a tomboy when she was younger, still more comfortable around boys than girls, she was the complete opposite of shy." Claim: "A bit of a tomboy when she was younger, still more comfortable around boys than girls, she was anything but a shrinking violet."
Considering the context, is the claim true, false, or unknown?