Period tracking for young girls

Violet
My niece has noticed a lot of changes that indicate her period will be starting soon. She is 10 and I plan to introduce her to <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">Eve</a> when she is older but I don't think her step-mom would appreciate it right now. Does anyone have an informational cycle based app for younger girls?