NIC maze

I am trying to sort out the remuneration strategy for a husband and wife (Mr and Mrs A) business which could trade as a limited company a partnership or husband with wife as an employee.

Mr A is four years older than his wife. My main concern is the National Insurance contributions aspects. Mrs A will carry out some work for the business and I am confident that I could justify a salary at least equivalent to her personal allowance. However she does have other investment income from property bank interest and dividends which currently would use between half and three-quarters of that allowance.
It did occur to me that as an employee Mrs A could be paid an amount that would result in a contribution record for no PAYE/NIC cost although there would be a consequent cost/loss of repayment on the...