@Kathy-and-Brian0 I'm sorry you're so distressed, but it really isn't a bad review at all- she says so many positive things about your place and your hosting and you are just concentrating on the one negative she mentioned. (I know the 4*s is a hard swallow) If no other guests have complained about the mattress, I might leave a public response like "I'm so glad you enjoyed your stay and sorry you found the mattress to be uncomfortable. No other guest has mentioned that issue, so we'll definitely be checking out what the problem might be."
I actually think she was quite low-key about it in her review and polite in her private feedback. She doesn't sound like a typical demanding complainer. I would also suggest that you actually go sleep there one night yourself. Just because other guests haven't mentioned it doesn't mean it might not be time to replace it. Another host posted here posted a similar guest complaint, for which the guests had actually checked out a day early, at least that's the reason the guests gave. When the host went over to find they had already left and read their note about the bed, he found that one of the bed slats had fallen out of place. It only a took a minute to put back, but the guest hadn't alerted him during the stay.
And if a guest says "between 2 and 3", I'd make sure to have the door code programmed by 2. it seems reasonable to me to give an hour window of arrival time to a host- they may not know if they might encounter traffic hold-ups, and when travelling with children, there always seems to be someone who desperately needs to stop and go to the bathroom even though you just left the restaurant and gave the "this is the time to use the bathroom, kids" lecture 10 minutes earlier, met with "But mom, I don't have to go" 🙂