pri vate duty nurse certificate of employment

I am a private duty nurse caring an invalid old lady for 6 months..The patient passed away last week and Im wondering if I can include my work as a private nurse in my resume..I received an honorarium of 7k monthly from the family, without deductions like tax, SSS, etc..Is having a letter of employment covering the date and the employers name with signature will be considered valid to be part of my experience?Is there a proper procedure in creating a letter of employment, so that it will not be looked upon as fake and doctored?please help me, Im looking for another job right now and Im hoping that my brief stint as a private nurse will be credited as an experience..thanks!