period? 10yr old step daughter

Not sure who to ask or what to say lol but my step daughter is 10 and I was putting clothes away and I seen her underwear had a odd colour on the inside so I checked and it was kinda red (white underwear) but it had looked like a pad or something sticky was also on it?, I'm just curious if she had started her period or what, I don't really wana text her mom cuz I don't want to step on any toes, maybe she just didn't wipe prober?, I took them out of her drawer to wash them....lol  any advice would be greatly appreciated:)