A shower is a lot easier with a long haired piggy. Sit them in the bath and run a gentle warm shower over them! Just keep it running over them the whole time and they will stay warm enough. Knots will simply have to be cut out as others have said - she will get upset if you try and tease them out with a brush as it will always pull. On a daily basis, try one of those cheap plastic combs you can get in places like Boots for keeping her hair matt free, works a treat.
Also, don't forget her 'trousers'! Even the shorter hair on their back legs gets knots.