I received a 1099-S for the Sale of My Main Home. Why?

I sold my mobile home for 43,000.00

The closing company issued a 1099-S to me and my mother (she had co-signed on my loan).  So we each got a 1099 for 21,500.00.

First, I don't understand why I got one in the first place, since its my main home and its under 250K.

Will the 21.5K be added to my INCOME number?  Im freaking out, cause I am a single Mom and my daughter gets State Healthcare.

And lastly, how will this effect my Mothers taxes, since she doesn't report interest or taxes on the trailer.  And that was the gross amount....we still have to pay off the loan anyway.

Any help is greatly appreciated.