@Kit45 I would message her back "Sorry, XX, I cannot offer any further discounts or waive the cleaning fee."
Then do nothing else. You don't have to either preapprove or decline an Inquiry (Booking Requests are different, you do have to Accept or Decline within 24 hours) at all- just messaging back is sufficient and you won't be dinged. You can safely ignore the proddings from Airbnb to pre-approve.
Try to be hard-hearted when guests plead poverty and ask you to discount. It's always a bad sign- they will go on to ask for more special treatment. A guest is a total stranger to you- their financial situation is none of your affair and it's disrespectful to you and your place to ask for a discount.