Not to sound cynical, but this is also a very good reason to have your BF there with you. What she hears through her fear may be very different from what you end up thinking you've said. It'd be good to have all of you there if she feels she needs support, or she thinks you've said something hurtful that you didn't intend to come across in that manner.
Not that your BF should have to be a mediator, but having his own interpretation of the talk (rather than getting a she-said/she-said version) will be a good thing.
Mono. Divorced, two kids (DanceGirl, 14; and PokéGirl, 11), two cats, one house, many projects.
My partner. Poly. In relationships with me, Xena, and Noa.
Poly. In relationships with Chops and Noa, and dating others.
Married, Poly. In relationships with Chops and Xena (individually).
Blog thread: A Mono's Journey Into Poly-Land (or, "Aw hell, there's no road map?!")
Slightly more polished blog with a mono/poly focus: From Baltic to Boardwalk