Maybe try leading with wide guard + surf? pixpix?
That might help with the field. pix~
Also, you have 3 mons that are really bad against charlotte, vik, decidueye and steelix(without sturdy). pix~ They are slow and will most likely be one shotted, consider switching vik and decidueye for more bulky pokémons, and switch steelix, or atleast its ability
Stealth rocks really destroy charlotte, sticky webs bother her too. pix~
Basculin and Tauros might prove useful here, not sure tho. pix~ You can use trick room cofagrigus together with a donphan from route 2 (they get earthquake really early). pix~ This basically kills every mon she has except rotom. pix~
X items work wonders on bulkier mons like cofagrigus. pix~