Cash is cash, nobody who wanted to be paid in cash would think twice about receiving a stack of £20s.
If she is depositing it into her bank account, the denomination doesn't matter. Deposit machines usually take 50 notes at a time, but if you have more you just do another transaction.
If she is not depositing them at the bank but spending them, £20s would be preferred over £50s anyway.
If she is going to the bank to deposit the notes, you should ask her if she will take the old pound coins as part of your rent payment. (You could give her £1 extra for the trouble.) A handful of banks insist they can only be deposited in bags of £20, but most aren't so silly. I think the machines in Metro Bank (which can be used by anybody) still accept the old pounds.
In the UK, ATMs (at least those operated by banks) are only limited by the card used. I have UK cards which allow £500 withdrawal per day. This can be "increased" to £1000 by going at 11.58pm, waiting a few minutes then making another withdrawal. I also have non-UK cards that have higher daily limits, I once did £2000 in one go (a long time ago).
I thought AirBNB is supposed to handle all the payment. Maybe she is trying to avoid some sort of AirBNB fees? Anyway, if she is paid in cash she knows exactly what she is getting and the guest knows exactly what to pay, whereas accepting paypal or credit cards incurs other fees that may not be straightforward to work out beforehand.
Last edited by :D!; Mar 9, 2019 at 12:36 am