Let's analyze the conversion:
Step 1: Identify the reporting verb and tense:
- Reporting verb: "said" (past tense).
Step 2: Modal verb "may" in direct speech changes to "might" in indirect speech when the reporting verb is in the past tense.
Step 3: Change pronouns as necessary:
Step 4: Keep the rest of the sentence intact as it is. Therefore, the correct indirect speech sentence is:
She said that she might buy a book on geography.