The options are as follows:
A. She met her friends in the lobby of the hotel, and they headed over to the pool for a cool, refreshing swim.
B. She met her friends at the hotel’s bottom floor, which is the lobby, so that they could head over to the swimming pool for a cool, brisk swim.
C. For a cool, brisk, refreshing swim at the hotel’s pool, she met her friends in the hotel’s lobby on the bottom floor.
D. The sentence is correct as written.
The best revision for the sentence is A, "She met her friends in the lobby of the hotel, and they headed over to the pool for a cool, refreshing swim."
It is not necessary to add that the hotel lobby is on the bottom floor. It doesn't add anything of value to the sentence and makes the sentence less readable.