If you leave a will, you're estate will go to whomever you wish to receive it. It doesn't have to be anybody in your family; you can leave it all to Battersea Dogs' Home if you so wish.
If you die intestate, then (assuming you haven't got a spouse or civil partner at the time of your death), your estate will be shared between your children. Your DIL won't be entitled to anything.
However your DIL could still indirectly benefit from your estate. If, after you've died, your son then passes away too (without leaving a will), your DIL will be entitled to receive all of his estate which will, of course, have been partly-funded from your own estate.