@Lauren157 Just for your info, when you answer another host just use the at key in your text so we'd get your mail 🙂
As much as I understand if you decline the change (you might have to give a valid explanation for that) she'll be booked for 2 nights and would have to cancel (hopefully some of the other hosts can back me up on this). HOWEVER, I would handle this situation very carefully!!! If she doesn't cancel, comes for 1 night and leaves you a crappy review (just picking on something) that might not be good. She has to stay at your place for that though.
Lets hope more experienced hosts would also advise you soon!