I assume the sedative she got was gabapentin otherwise that’s a suggestion.

Melbcat is usually very good but when she was first getting used to it I would tip the carrier onto its back end and gently drop her in. That sometimes buys you a second to shut the door before they rocket back out. A top-down carrier is also an option.

Another cat I had to trick by putting treats inside so he’d half go in and then quickly pushing his bottom in to shut the door.