Retired ICU nurse here and I see some wonderful advice on this thread!
Thoughts---you might want to look for nylon sewing thread for suturing purposes. It won't get wet like cotton thread and it seems to me that it would be less likely to harbor bacteria.
A curved (upholstery) needle would be good but I would look for the finest one available to reduce the size of the punctures.
If the wound edges are dry there is a good chance that they will not adhere to each other and will not heal. You might have to trim those edges back to fresh pink tissue before suturing to have them join together and eventually heal.
ITA with the penrose drain suggestion---there may definitely be an issue with fluid buildup if the wound is completely closed and there is no place for serous fluid to go. This could cause issues with pressure buildup on her organs and increased chance of infection. Do you notice fluid drainage from the area---either clear yellow, bloody, or pinkish?
No straight peroxide---we stopped doing that decades ago, going either to half peroxide and half saline or just saline. Straight peroxide actually destroys delicate healing tissue.
Open wounds can be packed with wet saline dressings, as mentioned previously. These sometimes do dry out a bit between dressing changes and should be thoroughly moistened before removing them as new healing tissue could be injured otherwise.
Sterile saline is ridiculously expensive.
Here is a recipe for saline that can be used safely to clean wounds and moisten wet dressings---keep it in the fridge:
https://www.ncbi.nlm.nih.gov/pubmed/17108769
You are doing a wonderful job---I hope your girl does well!