Her OBGYN will be the placed person to advise her on continuing Zoloft through pregnancy and I would be outside my area of expertise to comment on that specific aspect of her situation.
It does sound like she is experiencing obsessions so I will discuss them here before moving on to treatment options.
Obsessions are thoughts or images that are difficult to stop. An obsession is intrusive and normally seen as irrational, but the person is not able to stop or ignore these thoughts. Some common obsessions include the fear of becoming sick from germs, worrying about whether the stove was turned off when they left the house, worrying that something bad is about to happen to loved ones and worrying about certain thoughts that keep occurring. People often feel fear along with the obsessive thoughts.
Sometimes obsessions will be mild, only occurring once in a while. Other times
obsessive thoughts will be constant. The thoughts can sometimes intrude into a
person's daily life and are unwanted. Obsessive thoughts can interfere with
daily life, causing strain in relationships and in the workplace. When obsessions and compulsions become more extreme people can be diagnosed with Obsessive-Compulsive Disorder (OCD).
The good news is that obsessions are reasonably common and most definitely treatable. Cognitive Behavioral Therapy (CBT) is widely regarded as the gold standard therapy for obsessions and the National Institute for Clinical Excellence
recommends CBT as an effective treatment for OCD, see here. CBT is a psychotherapeutic approach that aims to solve problems concerning dysfunctional emotions, behaviors and cognitions through a goal-oriented, systematic procedure. Treatment is technique driven, brief, direct and time-limited (normally 10-12 sessions). CBT is used in individual therapy as well as group settings, and the techniques are often adapted for self-help applications.
Obsessive thinking is usually linked with a person's overall level of anxiety and so sometimes when a person is able to bring their anxiety levels down the obsessions diminish. Often obsessions become difficult to manage on your own and if this situation develops in her case then I would strongly recommend that she seek out a CBT trained therapist for an assessment and potential assistance. CBT is usually offered by Clinical Psychologists (although not exclusively) and she can contact the American Psychology Association for assistance in finding a suitably trained clinician. She can take a look at the American Psychology Association's locator service here . She can use this to find Psychologists in her area and there is a phone number she can contact if she wants a referral arranged. Also, she can take a look at an article published by the APA here. It's an interview with a senior Psychologist and covers some of the things she should consider when looking for a Psychologist.
She can make a start on by taking a look at some CBT based self-help material to begin learning some basic CBT techniques at home. Give her this document here
Also, I can recommend a book titled Coping with OCD: Practical Strategies for Living Well with Obsessive-compulsive Disorder and another book titled Getting Over OCD: A 10-Step Workbook for Taking Back Your Life. You can find both of these books on www.Amazon.com .
I hope this has been of some help. PLease let me know if you would like me t elaborate on any part of my answer of if you have further questions. Best of luck!