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"While going through our records recently, we found that your AdSense account has posed a significant risk to our AdWords advertisers."
"We have detected invalid activity on your site and your account has been disabled."
Unbeknownst to you, your sister may have shared your website to her friends and other relatives. Instead of helping by clicking ads, they end up having your account disabled.
What would be their incentive to lie?
Eggs in one basket? Sure. But the problem with Google being made the monopoly is that you end up getting forced to having them as the only source of eggs.
They've never shown any reluctance to tell people their AdSense accounts are disabled, and why. It's unlikely they'd go to the trouble over two accounts.
CTR ranged from 1% to 6% depending on the site and the season.
Number 1 rule of Adsense (IMO): never ever share your websites to family members or friends.