Java moss is a good plant to add to smaller 'hospital' tanks. It's proven to reduce ammonia buildup (not that there should be any, but still it helps keep the water nice) and doesn't mind lower/natural light. My little stunted guy (has never thrived) loves to sleep in his moss, and my female often 'fights' with it, as if she's playing in it.
You have a really nice little crowntail there. These fish really are incredibly tough.. sounds like yours has been through the mill and how. I hope she recovers now she's in better conditions.
The bubbles are pretty normal - even females will blow bubbles that stay on the water surface (especially in unfiltered tanks), though it's the males which make the spectacular bubble nests.
Clean, warm water and good protein-rich food (the mosquito larvae OFL suggested are brilliant) will do a lot to help this little one on her raod to recovery. Don't be surprised if she puts on a growth spurt after a few weeks of decent living conditions, though some fish exposed to terrible ammonia and waste early on never do grow properly and sometimes have ongoing health issues. My stunted fish will never be 'quite right' but we've kept him in the best health we can for six months now and he is as happy and healthy as we can make him. Of course, he is much loved.
Watch how this little fish captures your heart. Bettas are pretty special that way. =)