This seems like a good strategy..
But all you need to just a Fighting pokemon(Makuhita, Mankey, or Pancham[or Combusken/Monferno if you've chosen those pokemons for your starter]) A fire pokemon(you can get Litleo by trading off a Bibarel to a game in the Peridot Ward. You can also get Numel, a Fire/Ground type, in the North Peridot Ward when the weather condition is Thunderstorm), and Trubbish to get those two layers of Toxic Spikes. Flying pokemon is optional, but be sure to not use the flying pokemon against Cradily, because Cradily has the move Smack Down.
Step 1: Get your two layers of Toxic Spikes
Since Trubbish is a poison and Cacnea is the first pokemon that Florina sends out, he can resist any moves that she makes Cacnea use.
Step 2: Get your Fire and/or Flying type to defeat her other pokemon.
Step 3: If she sends her Cradily out only, switch out to your Fighting pokemon and spam fighting moves.
Cradily will need time to set up, so it's good to keep spamming those, and if your fighting pokemon dies early. Don't worry because of those toxic spikes the poison damage will continue to hut Cradily every turn by +6%.
Step 4(optional, if not been done): Clear out the rest of her pokemon(s) with your Fire and/or Flying type pokemon!