Shadows of her former self?

They could have wanted to hint she was a demon to a degree, hahaha.  
I haven’t seen the movie

@Background Pony #32D4  

 
Did you not read my comment? The shadow would be based off her adult model. Her adult model doesn’t have a horn. Then they would’ve had to miss that fact not once but twice when putting it next to said model and animation it.
 
No, the more likely answer is that it was symbolic. Her entire motivation in helping the Storm King was to regain her horn. This scene is during her solo singing about the things she’s experienced and suffered from. Her shadows having her horn isn’t necessarily an animation error.

@Vinyl Fluff  
or it could be an animation error.

Not only would her adult model not have a horn to begin with (which is what her shadow would’ve been based off) but the fact that they specifically gave her a double shadow with the horn means its much more likely to be intentional symbolism, as stated earlier.

@Binkyt11  
Hmm okay then. :-)

@Sky Blazer  
I don’t really care tbh. Thanks though!

@CountColtnackh  
You can be sure it even is a ‘he’ that posted, are you?

@Sandbag
 
 
@Binkyt11  

 
What he said

@Sandbag  
What her goal at the time was, to regain her horn. Not only that, it displays her inner feelings of how she feels.

@CountColtnackh  
People always say it’s symbolism, but what does it symbolise specifically?

I believe that was intended, actually.

I would never have noticed that ’til now! O.O

It’s called symbolism.