Concept:
The meaning of a word often depends on the context in which it is used. The word odd has multiple meanings in English.
Step 1: Understand the context.
The sentence says:
There was something odd about her behaviour.
Here, the discussion is about behaviour, not mathematics.
Step 2: Identify the meaning of "odd".
In everyday language, odd means:
• unusual
• strange
• unexpected
• peculiar
Step 3: Examine the options.
• Even: Opposite of odd in mathematics.
• Simple: Easy or uncomplicated.
• Strange: Unusual or difficult to understand.
• Familiar: Well known or recognized.
The word that best matches the meaning of odd is strange.
Thus,
\[
\boxed{\text{Strange}}
\]