Oh dear. I'm sorry you were ill, and I'm glad to hear you are on the mend.
As unpopular as I am about to become, I see one common issue throughout your posts that could be the reason DIL is distancing herself. There seems to be an awful lot of conversations between you, your DH and DS about DIL's behaviour. There also seems to be a fair bit of "tattling" by you and your DH to DS. I know you believe DS would never repeat any of these conversations to her, but honestly if they have a strong relationship, the kind you should want him to have, he absolutely does repeat every word to her.
If I were DIL in this situation I would also distance myself. However, her biggest problem is not you or your DH, it is DS. He needs to stop starting and/or humouring these conversations. She likely feels ganged up on by you three. She's not wrong.
If you can, I would also stop the "grandma competitions". You get weekly visits of a few hours, other grandma gets longer, non-weekly visits. Things can never be 50/50, but it actually sounds to me like they're pretty close. In fact, your DIL is even accommodating your request for more time. You just don't like the location. I believe you have valid concerns, but I don't believe they get to dictate where the visits take place. If the park your DIL suggested doesn't work, and it sounds like it doesn't right now, then just carry on with your other weekly visits.
Speaking of which, try to get over the "DS's house" issue. They have been living there for three years. They are raising their child there. It is just as much her place as his. I've never met you but your attitude on this comes through quite clearly.
While I don't think DIL is directing her anger appropriately at you, it is likely these DIL bashing conversations that are causing her attitude. She should be upset with DS, and I hope she will call him to task on it. In the meantime, I would suggest that you stop complaining, gossiping, tattling, and otherwise talking badly about her to your DS. If he brings her up, I suggest you change the topic. Because it's either you and your DH constantly complaining, or it's your DS playing both sides. Either way, DIL is left with three people critiquing and complaining about her every move, who then wonder why she doesn't want to spend more time with them.....