If the lady doesn't get divorced then it's absolutely essential that she writes a will, otherwise, in the event of her death, here estate will automatically pass to her husband (even if, by then, she's not even seen him for several decades).
At the moment she can't get a divorce anyway unless she can prove (or her husband is prepared to admit to) adultery or unreasonable behaviour. She must wait two years from the start of their separation if her husband agrees to the divorce or 5 years if he doesn't:
https://www.gov.uk/divorce/overview
However divorce would still seem the best way to go as she might wish to marry someone else later in life.