How would I address people who attend church with me?

A congregant is a a member of a congregation, so I might say “a fellow congregant,” though that does sound quite formal.

Here is Merriam-Webster's entry:

congregant n | con·gre·gant | \ˈkäŋ-gri-gənt\
: a person who is part of a congregation : a person who is attending religious services or who regularly attends religious services
: one who congregates; specifically : a member of a congregation

It's similar to parishioner. See this question for discussion of the two.

To take up the suggestion that Hot Licks makes in a comment above, parishioner might be an appropriate term for you to use. Here is the entry for parishioner in Merriam-Webster's Eleventh Collegiate Dictionary (2003):

parishioner n (15c) : a member or inhabitant of a parish

and here is the same dictionary's entry for parish:

parish n (14c) 1 a (1) : the ecclesiastical unit of area committed to one pastor (2) : the residents of such an area b Brit : a subdivision of county often coinciding with an original ecclesiastical parish and constituting the unit of local government 2 : a local church community composed of the members or constituents of a Protestant church 3 : a civil division of the state of Louisiana corresponding to a county in other states

So if definitions 1a(1), 1a(2), or 2 of parish apply in your situation, the term parishioner may be a good choice to fill in the blank in the sentence you provide:

A fellow ______ gave me a job at her business.