My mother inlaw is a very rude person,she favors our son?

over our daughter,my son is 23 and daughter is 22,but whenever she comes over she hugs my daughter and i like we have the plague,and if my daughter trys on something that shes all excited over just buying,she tells her its ugly and why did she buy that color and is always making sour faces whenever we talk,my husband says shes their grama and she can act anyway she wants and that they still better respect her, and that she deserves to have her kissed,i dont agree,if you give respect you will get it back,the kids put up with it and still act kind with her,as do i,but im really sick of it,and when i try to talk to my husband about it,he gets angry and tells me that shes his mother and he dont want nothing to be said about her,and he spoils her and waits on her hand and foot when shes around,and it just irks the s??t out of me!!he says shes older and deserves respect no matter how she acts and since we see her maybe 2or3times a month that we should just let her behavior p.