I found the cost of flea/tick medications was lowered immensely when I purchased them online and got the amount for the largest size animal it was sold for. Large dog frontline is safe for cats if you measure out the amt for the size cat you have. Cat frontline had more of one ingredient and the same of the others, so the cats didn't get as much as the one medication. It did not interfere with how well the medication worked for my cats at all. They got the same results as from the cat version.
If you are using a separate heartworm medication, please do not give them at the same time. I know several dog owners who ended up with serious problems because they did heartworm and flea medications at the same time. It was pesticide overload and one family lost two dogs to this before they figured it out.
You CAN use neem oil on pets very safely. It is an organic pesticide and i have been amazed by the results. Not only did it deal with a huge flea infestation, it also dealt with head lice. The resutls from head lice were incredible. I did the same for lice as for fleas on the dog. Put about half a teaspoon of neem in your hand and then mix with shampoo. Lather into hair and let sit for five min. Rinse well. Apply conditioner and use a metal nit comb to get the nits out. Then rinse the hair well. Plastic combs just don't work as well and the metal ones are worth the price. Neem makes the nits not stick to the hair shaft and it works better than the RID solution meant to loosen the nits.
Neem has a strong odor that is kinda yucky, but diluted with shampoo it isn't bad. It is often used in creams and lotions because it actually is very moisturizing and i have even seen recipes for cooking with neem - NOT something I would do, but some people seem to like it. It is VERY safe and often is used on organic crops. I have yet to find bugs it won't kill. Knock on wood, lol. You can get a few ounces of neem online fairly cheaply. We didn't use it instead of frontline, but sometimes frontline wasn't enough. I won't use OTC or rx medications for lice ever again, and I doubt my kids will on their children either. not unless neem isn't working. After using neem with shampoo for 2-3 days, and comping the hair carefully, we did not have problems 2 weeks later with nits hatching - the neem somehow interfered with them hatching into bugs.
For the yeast problems, you will likely have to keep an eye on them for years. You can probably use either plain yogurt or miconazole cream from the feminine hygeine aisle to help with future problems. I would just apply a little of the cream at the first sign of ear scratching because this can recur. Depending on the medication the vet gave, you may need to do this for several weeks. If you ever use the OTC cream, don't buy the three day or one day versions. they won't stay in place long enough to work on ears. Also keep an eye out for thrush in her mouth. Sometimes they can get that if they are susceptible to yeast infections.