Flea treatment for indoor kitty on a leash?

Okay, so Zissou and I go for walks on her leash a few times a week. There is a field behind our apartment and also we just walk down through the buildings. Anyway, as it's spring now, does she need flea/tick treatment for this? She rolls around on the grass, runs through bushes, etc. The only other cats here are two that people in the apartments behind us let out who look very well cared for and healthy, but there are rabbits, black squirrels, etc. I don't think its quite flea season yet here.

So, do you guys think I need to get her a prescription flea/tick/mite treatment? I see no reason for it aside from these encounters with the outdoors, is that enough?
We're not a super-heavy area for ticks, but they are around. I'm more concerned about that than the fleas, as I have some of the diatomaceous earth that I'd rather use and have found to be more effective than anything else.

I take Jamie outside on the leash every day, and we have a lot of cats and hedgehogs walking around our yard, etc.. I've never had a problem with fleas (touch wood), and just use a fine-toothed comb to look for ticks after we come back inside.

Bijou and Mika are taken out on leash (Bijou isn't leashed anymore - my husband and I disagree about this but he lets him out anyway and so far we've been lucky that nothing bad has happened to him). Because we can bring in fleas and other vermin on our clothing and Bijou can also pick up things, we use Revolution from April until November. Our vet said that since we had such a mild winter here this past year that the fleas didn't die off as they usually do.

A few weeks before I started bringing Abby out again, I treated her, and will continue to do so for the rest of the summer.