Hi!
I am very sorry for your loss. You are obviously a very caring owner.
Please do not separate freshly bonded piggies; that is even more upsetting and stressful for them! If your girl has become depressed in the wake of her companion dying, then taking the new piggy out, won't help any health issue.
Bonding and Interaction: Illustrated social behaviours and bonding dynamics
Unless we get a better idea of of the noises it is unfortunately impossible for us to make any suggestions, I am very sorry to say. Your information is far too vague to even start guessing.
You can link any video/audio into this thread that you have uploaded elsewhere on a public setting as we do not have a video upload on this forum, which is entirely member sponsored and relies on volunteer moderation.
Have you considered dry air from intense heating in the current US and UK cold spell? See whether a bowl of steaming water next to the cage does make a change.
But what I would strongly recommend is to weigh her daily at the same time instead of once weekly to monitor her food intake. See a vet is she has lost over 50g/2 oz and step in with syringe feed top up. Over 80% of the daily food intake is normally hay. You cannot check that just by watching her eat her veg (which is about 10% of what she is eating). That may show you whether there is indeed something going on or not.
The Importance Of Weighing - Ideal Weight / Overweight / Underweight
Complete Syringe Feeding Guide