If you are sure it IS definitely a yeast infection, then you can try Apple Cider Vinegar. Mix 50-50 with water. Distilled water is recommended but boiled water should be fine. When it's mixed warm the solution just a little to about body temperature. To do that safely you can just put it in a tiny bottle and keep it next to your skin for about 30 minutes. Then using a dropper, put two drops of the solution into the dog's ear canal, rub the ear in a circular motion, and then your dog will probably shake her body out. That's okay, the vinegar solution won't all come out it will spread about a bit in the ear canal.
If the yeast infection is also just inside the outer part of her ear, then bathe the inside of her ears with a cotton wool pad and some of the solution. This doesn't want to be too wet. You don't want too much liquid going down into her ear canal. I'd do that twice or three times a day.
A good way to tell if it's a yeast infection is -are her ears smelly and smell like old socks or cheese?
Obviously if she doesn't improve or gets worse, or shows any other signs and symptoms, then a vet is needed! Is there a low-cost clinic, or any charitable place you can take her who may look at her on a donation basis? Or anything like this that you could sign up for -in case of future times she may need the vet?
A bacterial infection ....it may smell worse. But don't take my word for it. It may not. It's just that there is usually a distinctive smell with a yeast infection.
There may be a bacterial infection going on in that ear. I can't say. If so she will need a course of antibiotics. That will prevent it going deeper into her inner ear and possibly spreading.
But try the Apple Cider Vinegar first and see if that helps. If you treat her ears 3 times a day, then I would give it about 3 days to see if there is any improvement.
If not, then the safest thing to do is take her to the vet one way or another.
I hope her poor ear is better soon.