[Daring Scylla]

First if I were you I'd hide my bows, i would
move things to an area that is either constently under your supervision or in a place that she is not going to find it - or if she does she has to come by you with the bows.
the items belong to you, even if she is family if you are above age 18 and an adult she cannot just take your stuff. no. doesn't work that way.

a lawsuit is going to cost much more than the worth of the bows, so i'd stay away from that. but you can report her for theft as well as telling your mum what's going on and how you intend to stop it. let her know, firmly that you intend to report her if she just up and takes your stuff. also let her know that she needs to find another way to pay her bills or ask for help. if she needs help paying, she should ask not take. explain it to her calmly and rationally and if she still acts badly take further action.
but don't bring it to a lawsuit it will cost way more than it's worth.
however if you do have a lawyer friend, you can get them to write a friendly but threatening letter to her. if she doesn't know you don't intend to carry out a lawsuit, that may stop her.
good luck.