Fork replacement for SR Suntour 29er
Been there and not done that. The only option I found was to go used, but even then, its hard to get a reasonably prices upgrade. A better option for me was replace the bike. For the price of upgrading the shock (at least $400) I sold my old bike ($300) and got an 'as new' bike that was much better all round.   

Accept that you are choosing to ride her cheap bike. Even if you upgrade the shocks, you will be still be riding a cheap bike..... before you know it it will be Grandfathers Axe (3 new heads and 4 new handles, but its the same axe my grandad used).