Anyone else not being able to beat Sindragosa?

I've been playing the upper reaches since it came out today and am having a serious problem trying to defeat Sindragosa. I beat Blood Queen Lana'thel and Professor Putricide in 1 go but can't for the life of me beat Sindragosa and I'm starting to get pretty frustrated.

I've had this game since it came out but being a F2P player and not really playing a whole lot means I don't have any decent decks which is really annoying. I've tried every hero against her but haven't gotten her below 13 HP.

The only decks I have that are somewhat ok are my incomplete C'thun druid, a mage deck without a lot of the essentials (I did get Frost Lich Jaina tho), and the only other deck I've done decently against her aside from those 2 is a hunter deck (got DK Rexxar). I also only have like 900 essence and not if I should get anything now or try to eventually get a legendary.

Anyone have any tips or suggestions on what I can do against her? I'm getting pretty frustrated so I'm just gonna take a break for a little bit. Any help would be greatly appreciated.