Only just beat Serra after about 30 tries, best advice I could give has been given, get drought vulpix, keep saving and reloading to get drought. The residual damage taken away from your team (and damage put on to jynx via dry skin) is very useful. My team that only just won: lvl 50 blaziken, lvl 50 scrafty, lvl 45 magneton, lvl 50 gyarados, lvl 28 vulpix, lvl 50 mr mime. I'd recommend starting by immediately getting rid of glaceon and leaving the abomnasnow (i found the glaceon to be slightly more problematic than abom. it's blizzards do a lot more).
Also might be worth getting something that can set up a light screen, in literally 30+ battles not a single blizzard missed in the drought so be aware that they will hit consistently.
This may seem elaborate but i did have a fair bit of trouble with this gym leader and maybe some other people are too.
Also youtube "nickaboo reborn serra" he managed to beat her in 5 rounds or something by spamming lava plume, and he sounds a lot like jonah hill so thats nice
