As a stay at home mom (of an almost 4 year old) who left the workforce due to relocating for my husband's job I can relate to your wife's situation. Being around other women in a similar life situation can be encouraging. Her feelings of isolation and being worn down are quite common, especially when one has a weak social support network in their life. It is great that you realize she needs some support and are attempting to share some of the responsibilities to help out.
What else could you do?
Ask other parents at the office whether they have any suggestions about what there is to do in the area, and how she could get out and meet other moms and kids for her son to play with. Many of the best things she could be getting out to do to break the isolation bubble are specific to the area where you live and what opportunities are out there. Some areas the thing to do might be hang out at the library. Or maybe there's a museum or zoo with an affordable annual membership. Or a playground that other stay at home moms frequent. Maybe there's a moms club or church group or other support group that already exists in your area. Pass along any suggestions that may interest your wife.
It is unclear from your post whether or not your son is in preschool or part-time daycare. If he is not (or sometimes even if he is, if he has high social needs!), he may be really hurting for social opportunities himself, and acting out when his needs aren't getting met, which is very exhausting as a parent to deal with. Making sure your child is getting ample social opportunities, exercise, and time outdoors can do wonders for reducing exhausting behavior issues. This doesn't have to be expensive classes. Taking him to the playground counts. Even better would be enrolling him in a preschool if he is not eligible for public schools, or joining or starting a preschool co-op. A friend of mine does a preschool co-op with 5 other parents, and the expenses are minimal (they purchased a ready-made curriculum) since they meet at each other's houses.
If there are kids your son plays with well at the park, encourage your wife to talk to them and try to set up a playdate in the future. If she's shy or having trouble reaching out at the park, perhaps go to the park together with your child on the weekend, and help your wife break the ice in talking to other parents.
Throw a casual event, such as a potluck or bbq lunch. Invite coworkers with stay at home spouses to attend with their families. Ask your wife to invite some acquaintances she's met in the last year. They don't have to be close friends (yet!). The idea is to reach out to other people she'd like to get to know better and create opportunities to connect.
Suggest your wife join a professional group, such as a group for writers that meets in the evening once a month, or a book club, or bunko group, or some other group where she might have some grown up time out of the house. Be sure to support making attendance possible by taking over child-care duties that evening.
Encourage your wife to find a mom's group in your area. Personally I prefer the kind that have regularly scheduled weekly playgroups. Then you don't have to worry about "dead weeks" when you're too frazzled to set up playdates. And these are often held at parks or people's houses so they are not expensive. There are national organizations like Mom's international or MOPS that may have a branch in your area. Or there may be a local group. Or a meetup group that does the same purpose. Etc.
Pick up local publications for parents. Often these are distributed for free at places of interest to families, grocery stores, the lobby of gymnastics centers, etc. These local publications may have event calendars and ads that give you ideas for stuff to do.
And lastly, spend time talking to your wife. She may just need an ear to listen to. Encourage her to call an old friend who's not local--it may just revive her spirit and give her some fresh energy.