You can teach Morrigan some heals (it's highly recommended btw), but she will always be stuck with the crappy Shapeshifter specialisation, while Wynne starts with the much better Spirit Healer specialisation.
I got through the game just fine with Morrigan as my healer though (using an assload of pultices, admittedly), so feel free to keep her as your healer.
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MvC3: Haggar/Ammy/Wesker
http://img.imgcake.com/1294368287999pngyz.png