Its certainly best to be honest, if they're a sensible landlord they'll do the credit checks on you mum too, you could always offer to pay for 6 months rent up front, I'm a landlord and I insisted on this and they paid up. Its not so daft, most people will know someone who can lend them 6 months rent, if they can't provide it, it either means they don't know anyone who can lend them which is unfortunate or knowone they know will trust them to pay them back which would have alarm bells ringing.