@Peggy Kelso congrats on the new venture!
First off, I am not an accountant or attorney...
I too have a vacation home in the Orlando area. It is highly unlikely that you will ever bring in that much income in one year. The main rental season is the summer and holidays, and if you brought in $1000 per week, you might see about $12-14K for the year. I also list on VacationRentals.com and its sister sites, and I have never received a 1099 from them. I know there are new rules for payment processing that requires them to do some sort of reporting.
I would think just document everything and if something should come up you can show that your sister reported the income and you are just managing it. I think you can set up what type of listing you are doing...owner or manager.
Maybe keep what you can in your sisters name, but you handle it. I have a manager that takes care of all business licenses and taxes for me. It is part of an agreement that I signed with him that he is allowed to do this on my behalf. Perhaps having some sort of agreement like that would be worth it.