She'd got Letitia's letters to refer to, and she could quickly have disarmed any suspicion by mention of some incident, or an inquiry after a mutual friend.
No, it was recognition as Charlotte that was the only thing she had to fear.
"She settled down at Little Paddocks, got to know her neighbours and, when she got a letter asking dear Letitia to be kind, she accepted with pleasure the visit of two young cousins she had never seen.
Their acceptance of her as Aunt Letty increased her security.
"The whole thing was going splendidly.
And then - she made her big mistake.
It was a mistake that arose solely from her kindness of heart and her naturally affectionate nature.
She got a letter from an old school friend who had fallen on evil days, and she hurried to the rescue.
Perhaps it may have been partly because she was, in spite of everything, lonely.
Her secret kept her in a way apart from people.
And she had been genuinely fond of Dora Bunner and remembered her as a symbol of her own gay carefree days at school.
Anyway, on an impulse, she answered Dora's letter in person.
And very surprised Dora must have been!
She'd written to Letitia and the sister who turned up in answer to her letter was Charlotte.
There was never any question of pretending to be Letitia to Dora.
Dora was one of the few old friends who had been admitted to see Charlotte in her lonely and unhappy days.
"And because she knew that Dora would look at the matter in exactly the same way as she did herself, she told Dora what she had done.
Dora approved wholeheartedly.
In her confused muddle-headed mind it seemed only right that dear Lotty should not be done out of her inheritance by Letty's untimely death.
Lotty deserved a reward for all the patient suffering she had borne so bravely.
It would have been most unfair if all that money should have gone to someone nobody had ever heard of.
"She quite understood that nothing must be allowed to get out.
It was like an extra pound of butter. You couldn't talk about it but there was nothing wrong about having it.
So Dora came to Little Paddocks - and very soon Charlotte began to understand that she had made a terrible mistake.
It was not merely the fact that Dora Bunner, with her muddles and her mistakes and her bungling, was quite maddening to live with.
Charlotte could have put up with that - because she really cared for Dora, and anyway knew from the doctor that Dora hadn't got a very long time to live.
But Dora very soon became a real danger.
Though Charlotte and Letitia had called each other by their full names, Dora was the kind of person who always uses abbreviations.
To her the sisters had always been Letty and Lotty.
And though she schooled her tongue resolutely to call her friend Letty, the old name often slipped out.
Memories of the past, too, were rather apt to come to her tongue - and Charlotte had constantly to be on the watch to check these forgetful allusions.
It began to get on her nerves.
"Still, nobody was likely to pay much attention to Dora's inconsistencies.
The real blow to Charlotte's security came, as I say, when she was recognised and spoken to by Rudi Scherz at the Royal Spa Hotel.
"I think that the money Rudi Scherz used to replace his earlier defalcations at the hotel may have come from Charlotte Blacklog.
Inspector Craddock doesn't believe - and I don't either - that Rudi Scherz applied to her for money with any idea of blackmail in his head."
"He hadn't the faintest idea he knew anything to blackmail her about," said Inspector Craddock.
"He knew that he was quite a personable young man - and he was aware by experience that personable young men sometimes can get money out of elderly ladies if they tell a hard luck story convincingly enough.
"But she may have seen it differently.
She may have thought that it was a form of insidious blackmail, that perhaps he suspected something - and that later, if there was publicity in the papers as there might be after Belle Goedler's death, he would realise that in her he had found a gold mine.
"And she was committed to the fraud now.
She'd established herself as Letitia Blacklog. With the Bank. With Mrs. Goedler.
The only snag was this rather dubious Swiss hotel clerk, an unreliable character, and possibly a blackmailer.
If only he were out of the way - she'd be safe.
"Perhaps she made it all up as a kind of fantasy first. She'd been starved of emotion and drama in her life. She pleased herself by working out the details. How would she go about getting rid of him?
"She made her plan.
And at last she decided to act on it.
She told her story of a sham hold-up at a party to Rudi Scherz, explained that she wanted a stranger to act the part of the 'gangster,' and offered him a generous sum for his cooperation.
"And the fact that he agreed without any suspicion is what makes me quite certain that Scherz had no idea that he had any kind of hold over her.
To him she was just a rather foolish old woman, very ready to part with money.