Bereaved depressed? GP, stressed anxious DD. What to do?

[TeenDivided]

As on the GP RIP post, one of our GPs had to be pts on Friday evening.
Remaining GP is 6 next month.

We collected a potential new friend on Monday.
She is installed across a partition, but introductions have not gone well with new going for old, old stressed and scared.

Old GP now has runny poos (we maybe gave her too much sweet stuff over the w/e) and isn't eating her nuggets at all (very unusual to be off her food).

We could
a) do nothing, hope she perks up when back to more normal diet of nuggets & green leafed food,
b) leave new GP across partition and hope they get used to each other
c) take new GP back to rescue and say not suitable, maybe see if a more placid one works better
d) take old GP to vet (would be stressful)
e) recognised old GP is sad and depressed and unlikely to perk up, and ...?

Not helped by DD having (clinically recognised) anxiety (which missed her a year of education 3 years ago, still recovering). So she gets massively stressed by this.

I'm sorry for the loss of your old GP and for your stress now . Is the new GP a baby or an adult? Same sex as your existing one or different? And did the GP you had to have PTS possibly have anything infectious wrong with them (so any chance your old one is actually sick as well as being stressed/scared of the new arrival)? Is the older one eating hay and veg and just leaving the nuggets or is s/he not eating at all (I'd be really worried about the latter, not eating at all isn't a good sign for GPs so if so I think it might be time for a vet visit if so)?

Sorry for all the questions but it's hard to know, it could just be settling in blip or something more worrying - how did you do the intros, have you tried bathing them both using the same soap/shampoo so they smell the same as one another? How is old GP when you handle him/her outside the cage/away from the new one, does s/he still seem down and scared or only when they're in the cage with the other one?

I know other people's anecdotes aren't always that helpful but when I've needed to bond new piggies I've often chosen babies as the 'new' companion rather than an adult as I think being smaller they're much less of a threat to the older pig, and if you have the space although it's counter intuitive I think it can be easier to introduce the one solo/bereaved pig to an existing bonded pair of younger pigs as the new pair play with one another and feel secure, they hopefully then don't get aggressive with the older pig. If you go up to 3 for a while that does then mean you don't have to go through intros all over again when the older one goes as well which is good.

It can just take a few days for everything to settle down though so maybe give it a little bit longer unless you're on the clock with the rescue for a return - have you called them for advice at all?

Thank you @maxelly some good things to think about.

Old one is 6, female. New one is supposedly 4, female, but way smaller than old.
Have just come back from the V E T who has given fibre and nutritional supplements. SShe's had some and has started munching a bit of hay again as well.

Interesting idea re bathing both, and having a friend for new one (she was in a group so we could potentially do this, but worried old one would then just be outnumbered!)

Yes have been in contact with rescue too.