I can only think of one reason why a reasonable person might object to a little girl having her toenails painted - and that's because they fear some freakish pervert out there who sees her might sexualize it, and use it as an excuse to sexualize her.
Now, bear in mind, I am about the most fundamentalist, hard-line anti-sexualization-of-children person you could ever meet. I find those weird 1990s kiddie-beauty-pageant things where they dress 2-year-olds up in very sexualized clothing with full glamour-make-up stomach-churning and horrific. I find hijabs on little pre-pubescent girls very similar (hijab is a practice of grown women who want to assert sexual privacy from men, and should have nothing to do with little kids).
But we are NOT talking about putting your daughter in full glamour-model face make-up here. And we're NOT talking about dressing her in sexualized adult-style clothing. We're talking about painting her sodding toenails with glittery nail varnish. ANYONE who sexualizes that is, by definition, sick in the head, and needs putting on a list that stops them going near playgrounds. You, your daughter, and your husband, should NOT have to worry about your little girl wearing a bit of glitter on her toenails.
Of course, even the youngest children, especially (but not only) girls, should learn about privacy and boundaries and protecting themselves from people out there who aren't always benign. But none of us should have to forgo every innocent bit of fun in our lives because there are bad people out there. There is nothing inherently sexual about glittery decorated nails, and anyone, of any age, of either sex, should be able to have a little bit of fun with that kind of thing.