Yes, Schwab is really good for the custodials. It's been a few years since I opened my kids' accounts, but the minimums at that time were $100. And then a minimum buy amount of $1 at a time -- perfect for a kid. We've been very satisfied with Schwab.
You can't go wrong with their S&P 500 Index Fund (SWPPX) or their Total Stock Market Index Fund (SWTSX-- fees are only .03% for both. Definitely go for a low-fee index fund, rather than an actively managed fund.
Good for you for doing this! Her future self will thank you.