If I read this correctly and your wife has a real dirt bike, buy a cheap dirt bike for you too, it'll be a lot cheaper in the long run.
Your tire options have been discussed at length in an endless number of threads here, but here is a summary:
Pirelli MT60 - Most aggressive, OE sized option. It's an SM compound in this size. Good both on/off road, doesn't last long if you use on road.
Avon Distanzia - Less aggressive than MT60, decent both on/off but more of a 90/10 tire than a dirt tire. In OE sizes it's an SM compound, see MT60 longevity issues.
Pirelli Scorpion Trail - Not very aggressive pattern, won't be good in mud or soft dirt. Comes in OE sizes and will probably outlast the former two by 2x, if not 3x.
There are a lot of other options if you choose to go with a rear tire mounted up front (120/90-17) and a 150/70-17 in the rear, these will be a lot more dirt oriented, will make it easier to deal with lose dirt and mud but will definitely will impact the street handling. If you like to ride twisty section at a good pace, not a good choice of tire. The bike wont handle as well, not to mention that these knobbies wont last that long either.
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