I do WBVs with my kids but in your case I would skip it. I wouldn't lie to get a sick visit in order to make up for a WBV. Not because I think it's morally wrong, but because IME sick visits go entirely different that WBV. Sick visits are more to the point. Doctor is often a bit more rushed because they squeezed you because after all the kid is sick

. The doctor isn't going to ask the questions they ask during a WBV and you're not going to get the opportunity to ask the random questions you might have because you are only there because the kid is sick. It's just not going to get much accomplished other than you will get your child weighed and measured, but there are easier ways to do that. My doctor will actually let people come in during lunch when they have no appointments to use the scale themselves. Maybe you could ask about that or just get on your home scale with and without the baby. Or perhaps the Health Dept. might do it when you get vaccinations?
Anyway, I can see how this being your first child this might be a bit of a concern, but I'm sure your little one will be fine. The important thing is you have coverage in case she does get sick or injured and will be able to get preventative care soon (that is a crazy rule by the way). In the mean time, you could call your doctor's office and find out what services might be available to you. Mine has a nurse line that is staffed 24/7 that you an call with questions, and it's free.