I am more old fashioned than many of those who have already answered because frankly unless you have offended her gravely at some time in the past, I think your DIL is being very rude, sulking in her room when she visits you in preference to spending at least some time with you.
However, on the bright side: your son, DIL and grandchildren do come to visit, so I would in your place try to be charitable and feel that your DIL feels comfortable enough with you to do her own thing rather than be with the rest of the family and pretend to enjoy herself. Hard I know, but saying anything will only make things worse.
How big is your son and DIL's home? Is she justified in saying you are under her feet when you visit?
Whether she is or not, book into a bed and breakfast or some similar not too expensive place next time you visit. If they comment, say you feel that the addition of two extra people is a little awkward. If they don't comment, say nothing.
Those who blame her behaviour on her poor relationship with her own parents are probably right, and at least you do see your family, which many don't because of some or other circumstance.