This is your second actual post.  Sorry the first one wasn't answered, this is mostly viewed by volunteers and not everything gets answered, although we try.

First of all, if your mother bought a mobile home and gave it to you, she is required to fill out a gift tax return to report the gift.  No tax is owed unless her total lifetime gifts are more than the $5.4 million lifetime exemption, but the gift tax return must be filed so the gift is counted against her lifetime tax-free limit.

Then, because this was a gift, your "cost basis" is the same as her cost basis when she bought it.  Cost basis is usually the purchase price, plus certain non-deductuble closing costs.  But cost basis is subject to other adjustments, and you may want to ask your mother or a tax advisor.  You need proof of the cost basis so you will need copies of her purchase documents.  The cost basis is also adjusted down if you claimed depreciation for business use of the home.

Then when you sell, you will owe capital gains tax on any increase over the cost basis.  If you lived in the home more than 2 years after owning it, you could exclude the first $250,000 of your gains from the tax.  Or, you can get a partial exclusion if you are selling early due to certain recognized hardships.  But even if you don't qualify for the exclusion, you would only owe tax on the increase in value.