Proper sentence

Use of preposition from is not proper. It should be "in".

Article should be omitted. 

From is used to indicate a starting point when there is some sort of movement.  You can remove a cake from the oven.  There is no movement of the cake while it is baking, so it bakes in the oven.

I am unsure why Rahul suggested that an article should be removed and disagree with that advice.  Both cake and oven need to have an article or some other determiner before it. 

My mother has just baked the cake in the oven.

My mother has just backed your cake in that oven.

Patty is correct, but I would remove 'has' (I'm always trying to remove extra words from my writing), and baking a cake imples that it was done in an oven...

My mother just baked the cake. (I would use this if she just recently finished baking it)

My mother baked the cake. (I would use this if she baked the cake yesterday, or before that)

Without proper context of how the sentence is being used, it is hard to determine exactly which one to use.

To answer your question, more info. is needed.  Is the cake baking in the oven?  Has the cake already been baked?  Is your mother taking a cake out of the oven?  Has your mother removed the baked cake from the oven?  The sentence is unclear.  If the cake is baking in the oven, you might want to write, My mother made the cake that is baking in the oven.  What is it you want to convey?  What are you trying to tell the reader?  My mother baked a cake.