Dies to Removal

Not easily. Using her activated ability puts her directly into play. You need a Stifle or a Trickbind to hit that.

Sounds like Derevi would be extremely good against the counterspells/big creatures guy. Can't be countered and taps down the creatures! She's very powerful when built correctly.

Gaddock Teeg is good, my wife plays it, but she often has trouble sealing the deal. With little card draw and a bunch of non-hasty creatures, I've found that it can be tough to force that last bit of damage through.