My husband had a severe wound in his leg, it would open up and puss would come out pretty reguarly.  The wound stayed open for several months and was painful.  Someone suggested that he get a tetanus shot.  He was not due for one and had had one 5 years previous.  He went ahead with the shot and within days the pain went away and had completely healed within a week.  Dont know if this will work for your situation, but might be worth a try.

unfortanetly I don't have much advice, but I do want to let you know you and your sister aren't alone. I have had open wounds on my leg since January.  It seems if we get them anywhere even close to healing they open right back up again. Mine have been cauterised 4 times also and it seems to make them worse.  I am working with a wound specialist also and really the only advice they have been able to give me is to was the area with a special soap called technicare and put a special bandage on it. Have you tried compression over the wound? I don't know if it is kind of swollen or not, but if it is compression can help because any kind of swelling in an area where you have wounds that don't heal right will cause wounds to stay open or reopen after they have closed.    I wear compressive socks to help with this, I know in the past I have gotten them on my back and they fitted me with a back brace to help with compression.  I don't know if I have been much help, but I just wanted you to know your not alone.

Brianna

(sorry for my bad english)
I will be carefull to give advices on this condition that she have. But there is a lot of diffirente wound/heeling bandage on the market and it`s very important that it`s right bandage/treatment for this type of wound/infection. I don`t know what bandages that are available on the US marked. 
At my job I have worked with many types of wounds and we have found out what type of wound/infection it is and use the spesefic bandage that are best for the wound and have got great results and also full recovering.

When you mention MRSA I got in mind a bandage that are effective barrier to antibiotic-resistant bacteria such as Antibiotic-resistant Pseudomonas, Methicillin-resistant Staphylococcus aureus (MRSA) and Vancomycin-resistant Enterococcus (VRE). The bandage are named Acticoat* (with Nanocrystalline Silver)^†.
Acticoat Dressing is indicated as an anti-microbial barrier layer over partial and full thickness wounds such as pressure ulcers, leg ulcers, diabetic foot ulcers, burns, recipient graft sites and cavity wounds.Acticoat kills pathogenic organisms in wounds to reduce the risk of infection. Acticoat is also effective in the reduction of bacterial load in wounds.

You said that maybe there is a tunnel inside the wound/near the spinal cord maybe that is an factor that the wound never closing?. I don`t know if this bandage is right for this wound so you HAVE TO talk to the wound specialist and get advice about bandages and more before you start up with an medical procedure.