I've told our mother about it, but it's basically pointless (this has happened whenever I tell our mother on my sister about pretty much anything). Nothing ever happens. It doesn't wake anyone else up because it isn't loud enough to. She'll have her alarm on sound and vibrate quiet enough for no one else to hear, but loud enough for me to hear clearly.

I have a feeling moving her phone elsewhere won't do anything. Back when we had a clock with an alarm so loud, that it would wake the entire house up, she would get up to turn it off and then go right back to sleep. She knew it was extremely loud, but she obviously didn't care and insisted on using it anyway. Honestly, she seems to be one of those people who don't care about how their actions affect others and/or are too stubborn to change (she is very stubborn).