I’m sorry about the loss of Pepe.
You definitely should not get a new companion for the mother bunny until after she has weaned her babies. That could be very dangerous to put another rabbit in with her now. It would cause a lot of stress to her and affect not only her, but the health of the babies. Any rabbit that you get to be a companion for her in the future will have to be bonded properly with her, and that is not always an easy task. Before bonding can be attempted, you will also need to spay your rabbit, as well as having any new rabbit spayed or neutered. You certainly can’t spay your rabbit until all the babies have been weaned.
I think that she will be very busy with the babies for the next several weeks, and they will keep her so occupied that there is no need to think of another companion for her at this time. Since you are keeping the babies, they will all be her companions for the future, anyway. Four rabbits can be a lot of work and take a lot of money. You will also have to separate the babies when they get to be about 3 months old, that is when they can start reproducing, and they can also fight when their hormones come flooding in. You will need to get all of the babies spayed and neutered when they are old enough – 5 months for the males, 6 for the females. Then after a month’s recuperation, you can start bonding the 4 rabbits.
Here are two good articles on bonding:
https://binkybunny.com/BUNNYINFO/tabid/53/CategoryID/9/PID/940/Default.aspx
http://rabbit.org/faq-bonding-multiple-rabbits/