For purposes of the mortgage interest deduction on schedule A, you can deduct interest on your main home and one second (personal) home. You must be a legal owner or the “beneficial owner” and be the person who actually pays the mortgage. (You do not have to be listed as a borrower, and we can talk about beneficial ownership in more detail if you want.)
If this is really investment property and you report rental income on schedule E, you would deduct the interest as a rental expense. But by investment, I think you mean a much more casual relationship where your mom lives there for now but you will take the profit when she moves out and you sell.
Also, you can deduct property taxes, but you must be the legal owner or co-owner against whom the tax is assessed and you must actually pay the tax. There is no beneficial owner rule for property taxes.
