Daughter-in-law. Her daughter’s father is her husband (she’s only been married once and is devoted, meaning she didn’t have an affair). This means John’s son is her husband, so John is her father-in-law, making her the daughter-in-law.
I can be quick and then I’m deadly, I am a rock, shell and bone medley. If I was made into a man, I’d make people dream, I gather in millions by ocean, sea and stream.
Sand. Quicksand is deadly (at least in movies). Sand is made up of rocks, shells and bones. The sandman visits you when you dream (again, according to legend, I’ve never seen him…) and there is plenty of sand in the oceans, seas and streams.
I have seven letters and am something you eat. My only anagram can help your pain. If you remove my first 2 letters I wear things down. Removing my first 3 letters is an adjective and removing my first 4 letters leaves a measure of time.
Sausage. You eat sausage, assuage is the only single-word anagram and provides relief from pain. Usage wears things down, sage is an adjective and age is a measure of time.