Just because you can't share the meal with her doesn't mean she doesn't deserve to have a delicious dinner. You can order her favourite meal to be delivered to her or ask someone who's local to bring it to her, whether it's your dad, a sibling, or one of your mom's friends. If you want her to go out, you could also cover the cost of dinner and plan for someone else to take her out in your place. In the past, I've sent my parents gift cards for various restaurants in town for them to enjoy a meal on me.