Since ABCD is a rhombus, we know that all four sides are equal in length and opposite angles are equal in measure. Let's call the length of each side "s".
Since BCE is an isosceles triangle, we know that angles CBE and CEB are equal in measure. Let's call this measure "x".
Since ABE is a straight line, we know that angles ABE and EBC are supplementary. This means that angle ABE has a measure of 180 - x degrees.
Now, let's look at triangle ACD. We know that angle ACD is equal to angle BCD (since opposite angles in a rhombus are equal) and that angle BCD is equal to 180 - 2x degrees (since it is supplementary to angle BCE).
So, angle ACD has a measure of (180 - 2x) degrees.
Finally, we can use the fact that opposite angles in a rhombus are equal to find the measure of angle DCA:
Angle DCA = 180 - angle ACD = 180 - (180 - 2x) = 2x
Therefore, the size of angle DCA is 2x degrees.