Is what my disabled sister pays me taxable income and what type of income?

If you are splitting costs 50/50 there is no need to declare income. Figure what you pay for rent, utilities, food etc. and divide it.

It is income and self-employment income at that. I assume you and your sister have a contract saying she is paying you so much a month. If so, then she needs to provide you with a miscellaneous 1099 to state your income from her. A contract is important if and when she needs medicaid for they will look back for 5 years and want to know what that money went for. Having a contract covers you in that situation.