Crystal Maiden (Waifu) is currently a very popular hero in the current meta game with a very high pick rate and a relatively low ban rate.
Her support and roaming potential is great with her Frostbite and crystal nova. Her arcane aura allows for this to be happening constantly.
When the time calls her ultimate ability Freezing field can have a big impact on team fights if uses correctly.

Remember that as CM you are a support, your allies come before you.
Courier>Wards>Items for yourself.