Summery: Rose Tyler lied on that beach, but not for her sake.
Authors Note: When people talk about how Rose lied to the Doctor in their 'final' farewell, they always say that she could be pregnant. This was born out of watching Doomsday, again, and thinking about how I would feel (which, I know, is never going to happen – how often do you hear about lovers being separated by metal men, pepper pots and levers?).
Lying
'There's still a Torchwood on this planet, it's open for business.'
It's a lie, but she can't bear to tell him otherwise. She says she's working and having adventures of her own, that she's making the most of it here in the-world-that's-not-quite-right. Instead she's doing the polar opposite of what he probably imagines. There's no defeating aliens or extraordinary technology or anything along those lines.
She can't bear to be within half a mile of the Torchwood building, let alone work there. She hates the organisations existence and cringes anytime Mickey or her pseudo-father mentions it. Her mother calls her stubborn but she knows that the real word is bitter.
Torchwood is the reason she can't be with him and she doesn't think she will ever forgive them. No matter which Torchwood it is, her universe or not, they're exactly the same. Her heart aches too much to associate with the company, so she simply doesn't. She'd be an 'asset' to their team and she's happy in the knowledge that her name will never be signed on a page that carries the organisations logo. It's her way of getting a comeuppance. Perhaps by not working for them it will punish the company the way they punished her.
Yet still she tells him she's not working in a shop, she simply cannot bear the look of disappointment she sees on his features. So she lets him believe she's doing exactly what she never will, if only because his belief may make their separation a little more bearable.