I wasn't widowed, I was left in my late 50s. I can say for sure that it was so lovely to be invited for a meal and/or stay over, it got me out of the house away from everything at home. I took every chance to make new memories, I know it is vastly different but it can be easier to think of other things when you are away from home, and there is one morning when she has company at breakfast.
She will never forget the times with her late husband at home, she won't be trying to do that, just make new memories and find a new normal
Maybe she thinks it's easier for you, she might think your husband would be bored if he came up too, whereas at home he can pop down the shed or something if he wants.
Maybe in the next few months there might be something near hers, maybe an exhibition or a concert , whatever, and you could ask if you could come up and stay .
Yes it's perfectly possible that she has got behind with stuff, maybe she has still got all her late husband's stuff around. And if she'd rather not but says another time try later