Hmm... adding to Meg/Lindsay said, I can add a slightly different option.
Thinking about the largest L&D/Children's hospital in my area, the BEST way to bypass normal ER admitting and security procedure is to come by EMS. (I've had 3 pre-term patients in the last 9 months-all went DIRECTLY to the floor and admitting met them there, rather than stop in the ER.) In the case of pre-term or imminent labor or delivery, the EMS crew will (ok, SHOULD) do a complete report before getting to the ED. Depending on the situation a team will meet them in the ED or we will go right to the floor. (Most ER staff is like, "Baby? Pregnant? Get the hell out of here and to L&D!!! Quick! Go!") The trick is to have something that gets you to the floor but not under the immediate attention of the staff etc. Pregnant people in labor get A LOT of attention.
So my first suggestion would be for your protagonist to pose as an EMS crew, not the patient. They are there all day, and the private transport crews take people OUT or to and from appointments all day, from all over the hospital. That is normal and rarely questioned. You can have someone on the stretcher or not. You can have them go to the victim's room, pretend they are they to transport or whatever... then the staff will have to go check etc etc. You might even be able to check the chart that way since EMS has to do a run report with basic medical info anyway, so they usually have to see the chart... again, wouldn't normally be questioned.
Another option is the "getting lost" approach. Go in as EMS, pretend you are there to pick someone up, OR are from out of town and dropped someone off and got lost getting out. Happens all the time in the big places.
(The same applies to wheelchair van transport.)
Depending on how accurate you want it, PM me and I can answer questions if you want.