Actually, Aunt Clare had been suspecting Howard Geoffrey ever since the incident where she was senselessly abducted and nearly drowned in a tank.
Aunt Clare always suspected that Rebecca Quentin might have been coerced by Howard Geoffrey, which would explain why she'd decided to stay by his side. However, Rebecca consistently denied it. Aunt Clare had to find another way on her own and finally thought of fabricating Rebecca's origins according to the last instructions Alexander Quentin had given before his death.
So, despite knowing that Howard Geoffrey might have someone watching her, Aunt Clare still spoke her piece in front of Alexander Quentin's urn...
She felt this statement would surely mislead Howard Geoffrey, because her fabrication was corroborated by a safe deposit box Alexander Quentin had previously set up in a bank.
