My suggestion would be to get some really good colloidal silver (such as that made by Utopia Silver) - put an ounce or more each day in the drinking water and, after cleaning the wound area with hydrogen peroxide, mist the colloidal silver througout the day and try to keep the are wet. That way you get the colloidal silver to the wound area inside and out.
Actually, the very best bet would be to get a bottle of ionic silver and one of colloidal silver. Use the ionic silver for the external area and add the colloidal silver to the drinking water. Your cat will love the silver in the water and probably regain some lost "friskiness" if she is more than a couple of years old.
Once the abcess begins to heal, you might try coating it with a good organic honey like Manuka Honey, but your cat may want to keep that licked off.
If you do decide to order from Utopia Silver, use the CureZone discount code of LR001 to get an automatic 15% discount on the silver or any other product if it is not on sale at the time.
DQ
Striveon's suggestions are great ones. If you don't have coconut oil or oil of oregano, GET THEM! Health food store colloidal silver is perhaps OK and you really, really do need the colloidal silver - but it will not likely be anywhere nearly as good as the silver from Utopia Silver.
I don't care how much you paid for the antibiotics, they are not likely to work as well as the silver and other items - though heeding mo123's advice on how to use them would likely be good, at least until you get the other items you need. I personally think that keeping the area lubricated in some manner to allow it to drain as much as needed would be a good idea.
If the antibiotics do not appear to be working, then you REALLY need the silver and other natural items.
You wanted help here and you have now gotten recommendations from a fellow member whose cat had a very similar problem (and they agree with the colloidal silver I recommended) So the solution you sought appears to be at hand.
Best of wishes for your tabby girl.
DQ.
You should have no problem finding oil of oregano and coconut oil. Probably collloidal silver too, though your best source would be Utopia Silver Supplements online.
If there is no more drainage (and don't force it), the colloidal silver will be very important, internally and externally, along with the oil of oregano and coconut oil externally. With that protective cone device in the photo, you also might use the organic honey too.
DQ