Inspect her really well for other wounds that may be hidden under the feathers, especially around the vent.
I would flush the wound with saline, chlorhexidine or if you don't have that, some warm soapy water (rinse well). Apply triple antibiotic ointment or something like Vetericyn. The feathers around the wound can be trimmed to help keep the wound cleaner and it's easier to see.
From what I can tell in the photo she lost some skin and feathers. Keeping the wound clean and moist with ointment a couple of times a day, generally a bird will heal o.k. and not need antibiotics. It takes some time.
If you feel you need antibiotics, then Amoxicillin would be a good choice. You can order those online dose is 57mg per pound of weight given orally twice a day for 7-14 days.
https://www.jedds.com/shop/fishmox/
For this type of injury, I would keep her separated so the other birds don't pick at it. Leave uncovered unless she really picks at her wound. Depending on where you keep her, if it's cold, then drying her well after rinsing/flushing the wound is important so she doesn't get chilled.
See that she's drinking well and offer her normal feed.