There's your answer to the inlaws staying.....dig the drive up, just tell the Mrs you fancy planting a few trees there.
I'll have a wild guess she wasn't even a HSBC employee. The wording of the letter states 'She’s been cleaning banks for 35 years' - so was she contracted by an agency. However, it certainly wouldn't have hurt to treat her with some dignity and respect. So I do take the point being made and no one is better than anyone, regardless of job.