I wouldn't cook two meals. The beauty of WW is that you can bank your points and have a splurge, using those banked points.
Now, if you were serving deepfried everything with 1000 calorie gravy, sure, she might have a problem with the meal.
But if you have a nice, balanced meal with sauces on the side as much as possible, she should be able to eat no problem. If she can't, it isn't your food that's the problem.
When issuing invitations to her in the future, I would tell her what the menu is, which sauces will be on the side and which won't. I would only make two concessions: have a big tossed green salad available and have some fresh fruit for her to have in place of a decadent dessert, if you are making one. She may want to budget points for the dessert but if she wants to save her points for the main course, she'd have an option.
And if she says she can't eat any of that, I would say, 'Sorry you won't be able to join us this time. Let's meet for lunch at salad bar next week.'