Girlfriend visiting on 6mth tourist visa

[bigfamily]

I hope someone can help answer my below question.
My girlfriend is a NZ citizen currently in the UK on a 2yr working holiday visa. I have indefinite leave to remain. Her visa expires the at the end of the year and she is going back to NZ.

My question is this: I am planning to leave the UK at the end of next year and would like her to come and stay with me for my last 6mths, so she would return to the UK after winter. She wouldn't work, I'd cover everything. What are our options? Will she be able to come in on a normal visa without any issues? Will the border staff not like the situation? Will it make it easier if she has a return ticket, bank statement printouts and a letter from me? Or should she come in with a 1mth return ticket, not mention me and push the flight out once in the UK?

Thanks in advance.