Puppies need to eat more. They also will relieve themselves more too though, you just have to be prepared for that. Two meals a day is really a minimum, most things I've seen suggest three meals a day. How you feed your doggies though is up to you and I'll respect that's not what you were asking.
On the note of what you were asking, it sounds like what you were doing before for your older dog was working...so...
If you think your older dog isn't holding it due to an increased feeding schedule then, and if what you were doing with your older dog before was working (feeding her once a day), perhaps you could continue it by feeding them in separate rooms? (Like feed one in the kitchen and the other (I'd suggest the puppy since you can close the door) in the bathroom). If you're feeding them in different rooms then they're not going to see each other eat and it would eliminate the jealousy. Dogs don't talk to each other in the same way we do, they don't run on up and say "Hay Max, still getting one meal a day? Yeah buddy! Guess what? Yeah, that's right, I'm getting two dinners. Oh yeah, mom loves me more." What they see, what they smell, what they experience, what they learn, and what they're conditioned to is what they know.
So that your older dog isn't seeing or smelling your puppy's extra meal, perhaps while your puppy is eating you could play a game with your older dog, or, if you need to work on resource guarding with your puppy then give your older dog a good chewy treat that's just enough to keep her occupied but not enough to cause her abdominal problems.
The puppy needs the extra-food, if the older dog was fine before but isn't now

then you probably messed up her routine, but to me that sounds fixable by putting it back to what she was comfortable with. Some of these multi-dog owners may have better suggestions for ya though

they're all brilliant with the stuff I couldn't have dreamed of no matter how much I try.