Sorry you have to feel so scared and alone. When I get in a bad situation, I try to remind myself that there are always more than two options. Two options are just an on/off switch, not choices, but there are always choices so I distract myself by making myself think of some? You know the old, "how many uses can you think of for a brick" exercises? Well when I am anxious or afraid I'm going to do something I'll regret later, I get myself involved in something else instead and often the feelings shift too. Feelings are like weather and eventually change and I pride myself on being a good "waiter" if all else fails, and just keep telling myself I can wait until my urges pass.

I would definitely take your mother-in-law up on her offer but maybe do a little thinking/writing about what subjects and things I might like to share with her? I would not necessarily talk about the urges to self harm but rather the stresses that feed the urges? Talk about when she was your age and ask her about her struggles and how she dealt with them? That way you might be able to get a better sense of her and how supportive or helpful she might be with some of your issues? Talk about loneliness "in general" and how she has dealt with the feeling in the past? You don't have to self disclose at first, there are all sorts of interesting, important topics that can be discussed with someone without being too personal and ways to get to know and converse with another better that are helpful.