To me it looks like a bumblefoot plug that is starting to be pushed out, but under the toenail. It is a little hard to tell from the picture. If it is bumblefoot, then soaking in Epsom and using antibiotic is perfect! Does it soften after you soak her foot? If it is still very hard, it could be a split nail. If it becomes softer, my guess is plug. Have you tried pulling on the plug/nail to see if it can be removed? If it is a plug that can be removed, fill the remaining hole with antibiotic ointment and wrap the toe as best you can. If it is a split nail, then I'm not sure what the best treatment would be.
If you aren't familiar with bumblefoot, here is a good link:
https://www.tillysnest.com/2015/12/non-surgical-bumblefoot-treatment-html/
Here is another bumblefoot link, but using a scalpel to remove the plug. I have only used a scalpel once when there was no scab to remove. I prefer not to cut healthy tissue unless absolutely necessary.
https://the-chicken-chick.com/bumblefoot-causes-treatment-w