Establishing rent-to-own with existing tenant

Hey all - first post and didn't find an identical topic so here goes:

I have a rental with a great tenant who I've had for almost 3 years. We really want to sell the place, but mostly want our tenant to buy it (she's expressed light interest) so I wanted to propose a lease-to-own agreement to her and see what she says...

Her rent is currently $1050/mo, and she's on month-to-month after completing her initial 12/mo lease. How can I structure this to be a win-win and make it attractive to her?

Rent credit is the part that confuses me when talking about an existing tenant - do I "raise" her rent by including a ~$200 credit, or keep it the same and essentially take a $200/mo hit if she ends up exercising the option.

Thanks!