how can i make my mother in law not feel offended?

Here is my situation. i work 6 days a week (saturdays being a half day get home by 3) ..and sundays off...

My inlaws live with us.

Every weekend I take my mother in law out-you know shopping or for a drive or whatever..Today I didnt feel like going anywhere as I just want to relax at home.

I did the groceries last night so I could have my sunday off and just be at home...in the area where I live going to Walmart is like a DISASTER!!! So much crowd and no parking!!!

Anyways today is Sunday and my mother in law is like lets go and I am like where?? and she is like walmart and i am like no and i tell her politely that i dont feel like going anywhere. today is my day off and i just wanna rest and get some housework done..

anyways she got angry and is like oh when you wanna go somewhere i go with u and now when i want to go u dont want to go...and i am like yeah but please try to understand i just want to stay at home...

anywyas she is upset iwth me and i told my hubby and hes lke dont worry about it and not to feel bad....

ok now hours later my father in law comes and is like y don tu take ur mother in law out and i told him my situation that i just feel like being home today and i told him y dont u take her out and he says she does not want to go out with me. my mother in law got angry and says that she does not need anyone and bla bla bla...what should i do? i feel so bad but i am really tired of compromising and being like a dog..when it seems like no one is considerate of my feelings...

PS: She has a drivers license and a car!! She is 55 years old.