Find out in advance how far along she is. That can have major impact on how you work with her, and what you need to be careful of.
If you really don't know much about bodywork for pregnancy, refer pregnant clients to a good MT that is well-trained in pregnancy massage. There is much more to it than massage technique, such as assessment, positioning, and adapting to the unique challenges of your client's physical transformations during pregnancy. Some clients have high-risk pregnancies and need special handling.
If you intend to work with pregnant clients in the future, attend a good seminar on pregnancy massage so you can proceed with confidence. I highly recommend Kate Jordan's "Bodywork for the Childbearing Year" - I learned an enormous amount in a short time and had great fun with it. My pregnant clients absolutely love the work I do. :grin: