Waffles is really a big puppy for six months old, so as long as she isn't having any health issues, then spaying her would not be a problem.
My Jilli Ann is six months 1 week old and weighs three pounds 6 ounces, so I have cancelled her spay till she's about four pounds because I'm like you, I don't want to take a chance yet.
I just hope she doesn't have a heat cycle before she's spayed, so I'll probably have this done next month.
I've never given any of my dogs medication for fleas, ticks or other parasites or insects and they have never had fleas, ticks, worms or any of those things. I've always used natural foods that change their body chemistry so that insects don't like their smell, even though humans can't smell it of course, and I use natural sprays I make myself to keep insects off.
Here is a good site for that:
Chinaroad Lowchens of Australia - Ticks, fleas, bees, flies, snakes and other gremlins! And how to deal with them!