The "all animals need a friend" thing comes first from humans being a social species themselves. It applies to herd animals like cows, sheep, horses, but with our inhouse pets it is not always true. Animals like cats or rabbits sometimes have public common meeting places, but may have seperate sleepingplaces unless with a nestmate or having young. Even when those sleeping places are close together, they don't live together 24/7, reason for forming a group is food (central place feral cats are fed in cities) and with prey animals safety during feeding, since they are then exposed and vulnerable. More eyes to see danger and less risk of being eaten.
Now for a 4 month old rabbit that is not yet mature that territorial thing may not kick in yet although females would be more likely to kick out another rabbit, because with kits they wouldn't be able to travel far for food untill kits are grown. So not having another rabbit munching on that food makes sense. Bucks are way more tolerant or they wouldn't get does to breed with. Castration/spaying can change those behaviours since they are also hormone driven.
Overall, some rabbits are very happy with a friend, some are not, maybe bad fit may be one not happy for any company. With a single rabbit in the house like here where contact with you is part of her life and in a sense part of her "job" the need for a rabbit friend is questionable. She is used to being alone and connecting with you, with a friend you as a human would be the third wheel in the relationship somewhat. Needed if they where outside, but inside? less so, provided you can keep her busy instead (toys and such help with that but yes time with you is needed).
I was wondering if she's okay by herself. I work a lot of hours. It just got her litter box trained and fear poop and pee all over my bed and couch again from another rabbit.
