Guinea pig questions?

my brother guinea pig loves to burrow in the covers so how can we mimic that in her enclosure? we hae tubes right now. also does she need a friend bc the petco employee said they only need one if you dont play with them alot and she said it right in front of my mom so i think it's close to impossible to get another guinea pig? lastly how can you litter train a guinea pig so you can just leave it out in your room while your in there? thanks