Hi. I'm Dr. Lee and will do my best to help.
What you are seeing is an abscess/infection of the elbow callus. Unfortunately, your only choices are either to use antibiotics on an as needed basis to keep the infection under control. It will come back however. Alternatively, she will need surgery to remove the callus and abscess and it won't come back. Topical treatment is usually not very successful for something like that.
Please let me know if you have any questions or concerns. Thanks.