My lady friend recently hinted at doing some BDSM. I was surprised as she is usually so prim. How do I find out if she is serious and if I should make the first move?
Well, it seems you may have a kinky lady friend on your hands! Let me start by saying that I'm happy to know you're interested in indulging her if she's into BDSM.
But now you need more information. BDSM includes at least three subgroups: bondage and discipline, domination and submission and sadism and masochism. That spectrum may not involve sex at all.
Based on her comment, I suspect you have an idea of what she may want to do. Open a dialogue and see if she truly is interested in at least trying it out. I suspect you will have many fun nights ahead of you once you start sharing your fantasies.