Your daughter should carry out market research to understand why demand has dropped for her property. Listings can have an artificial boost when they start on Airbnb so it may be falling demand/low season/or @Margaret--Rita-0 an oversaturated market. Or it could be her amenities or reviews. Only your daughter can understand what might be affecting her bookings.
Your daughter can do market research for similar properties in her area to see where they are advertising their properties.
Once she has this information she can set up her listing on these channels and invest in setting up her own direct channels so she can market her STR business directly @Margaret--Rita-0