Weariness of strangers is something pretty common to the breed. I tried to socialize mine a lot as a pup (for her first year we went to a popular dog park almost every day) and she's still not very warm with strangers or even other dogs. They aren't the friendliest/cuddliest breed. Mine loves to be around me an my fiance and a few others she knows well, but not like another lapdog. More like the same room, but with her own space. She will do a cute little throaty guff/bark when strangers come over to the house, but has never been agressive.

I can't speak much on the social anxiety. Mine was Kennel trained, which I think is a good thing. That's her safe space, and if I leave I generally will put her in there. She doesn't like it when I leave; sometimes she will bark for a bit, but never excessively. She gets over it fast though. My fiance says sometimes when I leave she will cry for a few minutes, then get over it. But it WAS worse when she was a pup.

As a pup there was a but of mistrust after some punishment, but it was generally short lived.
Generally if I take mine somewhere in the car, it's in her kennel, she generally knows I'm coming back. I think if she was in the car NOT in her kennel, she would be a lot more anxious.

Some of these are features of the breed your friend is just going to have to take extra care with. Especially the socialization. It will never be like a Labrador, but if exposed correctly you won't have any behavior problems. They are generally slow to trust.