I think this may be a case of perspective. I look at another parenting discussion site and many parents and couples there say they have in-laws who come to their homes (often uninvited) every single DAY, and who would find twice a week just fine. And some talk about how the in-laws have zero life of their own, no activities, no hobbies, no volunteering, and who depend utterly and totally on their adult children and grandchildren to provide 100 percent of their activity, all the time.
So to them, your situation would sound idyllic.
Granted, it's not idyllic to you. Can you step back from your emotions enough to try to think about why you're so wound up over her? For instance: How precisely is she "overinvolved" when she sees you those two times a week? Does she give advice on how to raise your kids (not sure if you have some), does she try to intervene in decisions about your husband's health issues, does she nitpick or make comments about your housekeeping or cooking, does she complain that you should see more of her, etc.?
If she does any of those things, it's your husband's job -- each person should deal with his or her OWN parents -- to talk to her kindly but firmly and say things like, "Mom, when we have health news to share we'll share it with you, so please stop asking; it increases my stress to be asked weekly about health details" and so on for each thing.
But if she doesn't do those types of things, can you pin down for yourself what is the exact issue, other than spending time with her weekly? You do mention that your own parents are far away and you see them "two times a year and that's plenty," so it sounds as if you arent' keen on anyone, your own parents or in-laws, seeing much of your and your husband. If your husband was raised differently and is fine spending time with her or other relatives, is it possible that he was raised with family around and takes for granted that folks will just see each other frequently, but your own upbringing was unhappy, or you just aren't close to your parents, then maybe his background and your background mean you don't understand each others' attitudes about spending time with parents. Neither attitude is wrong, and you can't help how you feel, but you can try to see another perspective.
And you can engage a lot of ways to see her but keep it more on your terms. If twice a week is too much, cut it to once; be too busy with an activity the next time she calls and wants to plan something. She wants to come over Wednesday? "Sorry, it was great seeing you Monday, but Wednesday I'm busy. Lt's meet next Tuesday instead." Say no, and then give an alternative that works for YOU so she doesn't feel cut out but also doesn't have a chance to say, "How about Thursday this week?" insteadl
You refer to her as "wonderful" and say you don't have a problem with her but seem to have a problem with spending time with her. You may just need more time alone than she does; she may be more social overall or the type who gets out and goes, goes, goes when you're not that way, but it doesn't make either of you right or wrong. She just may need some kind "No"s said to her. But take care you don't push her away or make her feel she's not wanted, especially if she is indeed a wonderful and involved person. She might be there for you someday if things get tough or your husband has health issues that mean you're swamped and need help. Just think about the things that you feel are wonderful about her and focus on those, along with learning to say no, which is easier to say when you do have other activities yourself.