It can be very hard to watch the ones we love suffer a loss as devastating as the death of a spouse. Your concern about your sister, and your desire to help her, are both admirable. As her sibling, you probably have a good idea of how your sister likes to live her life and you can use this information as a segue to discuss your sister s current needs.
Very often the bereaved will not be able to answer a question as broad as how can I help? or what do you need? Instead, it can be up to loved ones to try to figure out what they can do to ease the burden. For example, if you know that your brother-in-law was the cook in their household then you might tell your sister that you d like to bring some frozen dinners by, or suggest that the two of you attend a cookery course to get out of the house.
It may well be that you need to turn these suggestions around and make it sound like she would be doing you a favour in order for her to accept. This might be from pride, it might be because she doesn t realise she needs help or it might be that she doesn t even have the energy to spare figuring out her own schedule. Whatever the case, offering something specific is a good way to start.
Now, however, is not the time to discuss the fact that your sister does not have children and that you believe that you are all she has. Your sister obviously realises that she no longer has her own family, and if she wants to discuss this with you then chances are she will.
If your sister seems exceptionally low and you are worried about her then you might consider telling her this, using specific examples where appropriate. Sometimes people do not realise what their actions are conveying to others, and sometimes the bereaved need someone else to observe their behaviour before they realise it themselves. If you feel that professional help is needed, such as the services of a member of the clergy or a trained bereavement counsellor, then finding out information and discussing it with your sister will let her know that you care.
But remember, you can not force help on adults who do not want it. The best you can do is to help your sister in the ways that she asks, or continue to suggest ways that you would like to help. Over time it s likely that you ll both work out what part you will each play in each other s futures.