Yes, you can order at a TS while she doesn't, except at buffets (where it won't matter anyway, since she has credits to spend on her own). If you don't want the food but would like to get her a beverage or maybe part of her "meal" (just the cup of soup, for example, or just the french fries), the servers could manage this for you and use her credit for it rather than charging you. Just because she has a meal credit doesn't mean she has to order an entire meal. And again, she doesn't have to order anything at all.
My mom and I frequently split meals when travelling to WDW together, nobody ever says a thing and many places bring us the meal already split on two plates.
For QS meals, you can order her a kids' meal and choose the grapes or apples or carrots or the cookies as her sides - these are fully packaged and can be carried with you for munching on later. If the location carries the PB&J kids meal, that uncrustable can also be carried away if she doesn't want to eat it. Otherwise, she can just eat the sandwich/pizza/etc and take the rest off with her to eat later. And of course she is not oliged to order anything at all, and you can leave her credits unused just like the TS ones.
She can of course eat part of your QS meal as well, if that is preferred, but this is a way to use her credits for things that may work better for her eating style - to be eaten in little parts over time rather than needing to finish it before you leave the restaurant.