There are usually two ways of suiciding your shaman.

 

The first way is simply by selecting her, and clicking on some unreachable place (this could be near water - shore - or on a unreachable island or step hill). After some seconds, if she doesn't move, she will start losing health, and eventually dies.

 

The second way is way faster, and requires a spell (this does not work if you cast landbridge, armageddon, or teleport into a really close location). Get your shaman near water (on the shore, or beach), and cast a spell. As she jumps, press "D" once. She will cast the spell and move to water, dying. This process is similar to the "Falling from Cliff" trick, which you can read on F.6 area.

 

Suicided shamans will reincarnate faster than normally killed ones.