If you are satisifed that her main residence is in the UK then you have to include her on the claim. If she has a holiday visa it will say something along the lines of 180 day limit, no recourse to publuc funds, work prohibited. In that she is subject to immigration control due to 115(9)(b) so is not exempt from the NINO requirement. Due to this you need to send a DCI1 to the DWP to apply for a NINO for the partner. She will need a NINO (or to satisfy that she has taken every effort to obtain a NINO such as attending interviews at the DWP) for the period of her VISA. It depends if she applies for further leave to remain as to when the requirement to satisfy the NINO conditions will end.