I'm by no means an expert, but I can relate my experience and what I learned. My daughter had an abscess at her TI about 5 months ago. I'm not sure if antibiotics will work for you, as the abscess is a fairly thick sac, and the medication can't seem to penetrate it. In her case, and from what I understand the common treatment is, to have the abscess drained, and then leave a drain line in for about a week. Then antibiotics can start to work on any infection left over. Usually Flagyl. The complication with this is there might be a fistula attached to the sac. This is the case with my daughter. That can be stubborn to heal. Once again I'm no expert. I'm sure others here will chime in and give advise. Good Luck with the treatment. Do not let this go too long, as you wouln't want the abscess to burst.
As of right now, we're still not sure if her fistula is totally healed or not. Fortunately, it never came to the skin, as it stopped at the abscess sac. The Dr.s were somewhat concerned about a recurrence, but felt that with medication it has a chance of healing. She's been on Imuran for awhile now, which is suppose to have a positive effect on healing fistulas. She was also on Flagyl for quite awhile. She goes back in the middle of June, and they will likely do another SBFT to see what the state of things are. Our GI had suggested Remicade as well, but like you the biologics really scare me. I don't know of any natural approach specifically for fistula healing, but it would be great to come across something that worked. Good Luck with the treatment for your daughter.