If the goal is to blow her up, the other thing you can do is lower her activity. Use moving in as a chance to take over or outsource physical tasks.
Hire a housekeeper. Frequently stop into the grocery store on your way home. Reduce the intensity of physical dates. Maybe replace a nature hike with a nature center. Or drop her to get a table while you find a spot.
She's gonna run into the limits of her physicality with an extra hundred pounds. So these changes have the added benefit of minimizing those moments.
Encourage her sedentary interests. Even better if you can tie them to eating with others. Book club that meets at restaurants. Girls trivia night at the bar. Maybe the local food pantry does a gourmet charity dinner.
Nurture identities that naturally send your calorie needs in opposite directions, in other words. If it's who she is, changing requires far more sacrifice than eating a little less. It means losing relationships, belonging, identity.
Or ya know, enjoy the ride and don't worry about it. What's it matter if you carry an extra fifty for a couple years.