DS had it last month and I'm pg (28 weeks when he became contagious).
Here's what my obstetrician said:
If you had it, you will not be infected.
Your immunity protects your baby.
In the first trimester the chance of passing it on to baby is there but quite remote if the contact with infection is not prolonged (IE your friend should be OK, but you would not be if you had to care for a sick child.
The protocol at that stage of pregnancy however is to have the test to check for immunity. Tell your friend.
On a positive note, 80 to 90% of the adult population carries the virus even if they do not remember having developped a case of CP.
Middle pregnancy no major problem.
Very dangerous if contact with CP in the last weeks of pregnancy because if the mother carries the active virus at birt the baby is infected and condition is extremely dangerous for newborns.
All in all, there is a high probability she'll be OK but it's for her doctor to say, not us!