Quoting iLL-Legal Alien:" MIL was in 2 out 3 of my deliveries. For the one she wasn't in, ironically she was working in the ... [snip!] ... 2. And DH pretty much acted as if she wasn't there either, she didn't take any attention from me, the baby or the experience."
sounds like my MIL. she came in spent the entire day and night with me after i had my son (hubby was in afghanistan) she was a blessing. i was stuck on the L&D floor because i was pretty sick and still had my IV and junk. She was an amazing help, and would basically melt into the woodwork and read her book and not bother me until i wanted/needed her. she was very proactive in making sure my son and i had the best care possible. it was nice having her there.
so OP, really reconsider, it might be a huge benefit to you having her there, or if she's a pain in the ass... boot her out. its nice to have a person to run errands, get coffee, etc. if you're not comfortable with her seeing your vagina have her up by your head. there's a very small period of time when your "spread eagle" as you so eloquently put it.