Hi Tita,
I think your kindness for both your puppy and your roommates dog is really great. I wish I knew more about what the Pink Lump is to help but unfortunately I'm not a Vet....

Personally, I think your doing the right thing in regards to being concerned. I personally don't think it's probably contagious but your Roommate should get it checked out if the PInk Lump has been there for longer than a week and it's not getting any better.
Does the lump have any fluid in it or is it just more of a "BITE" or bump of some sort? How big is the lump? Let me know and I'll ask a few friends and see if they can't login here and help out.
Thanks! (and welcome to the site!)