Hi Other Angel! Great questions!
So first, a doula is essentially a pregnancy/parenthood assistant. You might hear them mentioned in the same spaces as midwives, who are licensed to actually handle the medical parts of birth-giving. A doula handles physical, mental, and emotional support for people who are expecting. A midwife is called upon when it's time to deliver the baby, but a doula can assist the parent(s) at multiple stages, including when people are seeking an abortion, have had/are experiencing a miscarriage, are considering adoption, or are post-partum (post-birth). A full spectrum doula performs multiple or all of these roles!
Second, on pronouns: generally speaking, a person who goes by they/them pronouns may be expressing gender variance of some kind. Some people go by just they/them, while others use multiple (she & they, for example). You would have to ask your friend how she feels, but this might indicate that she's going through a gender journey and is considering using different pronouns in public. Our founder Heather has a post about using they/them pronouns here: For the love of they, them and we who use them.
I also found this article that might help you understand why someone would change their pronouns: Use Your Words: The Language We Use to Describe Ourselves Matters