Experienced owner with a problem I've never encountered before..

I guess I should start off by saying I am the proud owner of 5 beautiful and super healthy girls. I have been adopting and raising guinea pigs for quite some time now, but recently I have encountered a problem I haven't before and haven't heard of. I'll try and explain as best I can as I have two of them claiming most of my attention right now and its so hard to ignore them

Well about 2 years ago we adopted a guinea pig and named her Scarlet. She was very sick when we got her, but that's also the reason we did. I knew she was sick and I had the means and experience to get her the care she needed for a long and happy life. Her illness was very bad and she required round the clock care that my fiancee and I were happy to give. I worked a lot so he was with her most often so naturally she bonded with him more...her death has been hardest on him. We took her to our vet who specializes in small animal care and in a few weeks she was a normal and happy baby, but the vet told us the illness was so bad it had weakened her immune system. So naturally we were always aware of her health and made the cages and their room as clean as humanly possible, but every now and again she would get sick, but we always cured her. However about 6 months ago to the day she was showing signs of illness once again so we made another appointment. I could tell this time it was bad, but towards the end of the night she looked fine so I put her back with her sisters (note: she was not contagious or a danger to her sisters. I made the vet be 100% sure and she was miserable in the isolation cage) Anyways she was fine for about a day then all of a sudden the next night she was worse than ever. After both of us cuddling her and holding her for hours we kissed her good night for the last time and I told her it was okay to go if she was in pain and that mommy and daddy would see her soon. (tearjerker I know) Truthfully I had myself believing that the next morning she'd be fine, but she went and we were devastated. Burying her was the hardest thing I've ever had to do and I've been through more than the average person. She had a fear of the dark and putting her in it really messed with me.

The problem however isn't her death its one of my other girls, Roxanne. I noticed how her entire behavior changed after Scarlet's death. I would think its her grieving, but the thing is I never saw those two bond...EVER. Granted they got along just fine, but they definitely didn't seem as close as some of my other girls.
Before Scarlet's death Roxanne was a very happy go lucky guinea pig, got along well with her sisters, loved floor time and her individual time with my fiancee and me. After the death I noticed her slowly start to change. She acts terrified of the sisters she once cuddled with..literally if any one of them comes near her she either screams her poor head off or becomes extremely violent (more than a little nip like most..its terrifying to see) Now when they have floor time she either runs to a hiding spot or tries to climb back in her cage and acts like she's having a panic attack. I've tried slowly reintroducing floor time away from her sisters in a smaller part of the floor so she wont be so overwhelmed, but its always the same thing. She doesn't seem to enjoy her fruits and veggies..I mean she eats them, but its just not the same. We've had her checked and she is 100% healthy and I just can't figure out whats wrong. Part of me thinks its because Scarlet passed away, but a nagging feeling makes me think its something more. I've read about how guinea pigs grieve and I've never read about them acting this way. I'm just so worried and want her to be happy, but I have no idea what to do

Anybody that has had anything similar happen or can give me any advice I would really appreciate it. Also if anyone has any questions or problems I'd be more than happy to help if I can
Thanks
I've attached pictures of both girls. The one on the left is Scarlet and the right is Roxanne