I have several thoughts as to what might be going on with Ellie's foot.
Interestingly enough, I saw a patient yesterday with a very similar mass on their toe in a very similar area. My initial thoughts about this patient...and for your lab as well....are as follows:
1. A cyst which would be benign...and most commonly seen in a dog this age.
2. A small abscess or infection
3. Possibly something more serious such as a mast cell or other cancerous lesion, I'm sorry to say.
It is often not possible to determine what a lump or bump might be based on feel or visualization alone; therefore, in these situations, an aspirate of the contents with staining and examination under a microscope can often be quite helpful in trying to determine what this lesion might be. If #1, then non-specific debris and a few cells might be seen; if #2, then pus and white blood cells are usually present. If #3, then different sized cells (indicating rapid growth) or granules (suggestive of a mast cell tumor) or other changes in the cells might suggest something more problematic.
And, when it comes to treatment options, we are somewhat limited....we either monitor them, freeze them off if small enough, or surgically remove them.
I'm glad you're having her seen tomorrow, but in the meantime, I do have a few suggestions which may be of help:
1. The foot can be soaked in a warm Epsom Salt bath for 5-10 minutes twice a day.
2. If she's not vomiting nor currently taking steroids or any non-steroidal anti-inflammatory medication, then Aspirin can be given which may help reduce any inflammation which is present. The dose would be 10 mgs per pound of body weight twice a day with food to avoid stomach upset. My only hesitation about its use would be that it might interfere with what your vet might want to prescribe but one or two doses won't be harmful.
3. After you dry off her foot, if you'd like to continue applying antiseptic cream/ointment to the lesion, this won't be harmful at all. Just distract her for 10 minutes or thereabouts so the cream has time to be absorbed. It won't necessarily harm her if she licks it off, but the cream won't be effective if she does.
I hope this helps. Deb