Please tell her this is normal, and even with a nice big house, the 16 yr old is probably feeling a lot more internal conflict than the little guys. Further, I think that a lot of people feed in to "one big happy" and push "puree" on the family blender and all that gets you is a M.E.S.S. Not that stepfamilies can't be successful, but you have to acknowledge where each member is coming from. Just because Mom gets along great with her husband doesn't mean the kids will. She really needs to give her daughter a break and if it is her husband complaining, say the same to him. Relationships have to grow naturally.
My 21 yr old stepson and I don't have long detailed discussions. It's not our relationship. But we get along, and he has a good relationship with his dad and they talk often. It can be hard but sometimes you shouldn't sweat small things. Your friend should enforce basic respect between all parties, but recognize that they have to give each other time. Stepfamilies often need 7 or more years to really gel. If she just recently got married and got divorced when her daughter was 12...that's a lot in a short and very important time in a kid's life.
I don't know from this if the mom is more worried about her daughter in that she's being distant to her SF or if the mom is looking for validation in her choices through her child's behavior. If the mom is looking for validation in the children, she needs to ask herself why. Especially if it's not really a problem.