oi...
um, thing is, from a female perspective perhaps...
you'd be doing her a big favor (provided she actually takes it to heart) by telling her why you want to let her go.
of course, it's kind and gentelmanly of you to not want to hurt her further, i do admire your kindness
but, this will keep happening to her unless she gets rid of her baggage. whether she does or not is obviously her choice and responsibility...but maybe she needs to have her eyes opened to it's existance?
i dunno. i could be wrong.
but i don't think 'letting her down easy' is necessarily going to help her in the long run.
whatever you do, however u do it, good luck!