This is not about her "not wanting" the help. This is way beyond that. This is a chemical imbalance and a true medical condition. As Jill says below, you can't entertain people so they snap out of it, any more than you can tell a nauseated pregnant woman to think about something else or a sick chemo patient to just cheer up or someone with pneumonia to just stop coughing. It's equally fruitless to tell someone addicted to drugs (legal or illegal) to "just stop and turn in their drugs." Same with cigarettes. It's just not simple like that.
Checking in is a good idea so that you can hear any cues that she's nose-diving and in need of immediate medical support, but that's about it. Also, people with severe depression are often exhausted, so these outings or play time with an active child can be a huge physical strain on them. None of this can be expected to "get her out of her funk" or "work" against a disease resistant to treatment.
I'd be curious about what's in the shakes and what types of vitamins she's taking. Some are great and others are totally ineffective and just throw off the balance even more. If the shakes are full of emulsifiers, for example, then she could be filling up on stuff with no nutritional value and that's blocking the absorption. Most commercial vitamins, especially in pill form, have too little included or too few ingredients to make a significant difference. I did take some phenomenal shakes that helped me beat my depression, but I had great customer support and was able to stick it out for 5 months to get great results. Expecting things like that, or even medications, to work in a few weeks just isn't reasonable 99% of the time.
I do think it's a good idea to have other conditions ruled out to be sure there aren't multiple factors at play here and also to be sure that drugs for one condition won't interfere with another illness. Make sure there's a good team working together and sharing information (with all consents signed). If possible, have someone go to every medical appointment and take notes. When my husband had a very mysterious disease (looked like heart failure but wasn't), the only thing that tied everyone together was my big 3-ring binder with copies of test results, names/numbers of every doctor, dates of service in several major hospitals, and 5-times-daily blood pressure readings. Sometimes hospitals/doctors don't fax things in time or files can't be opened (can't tell you how often that happened), and it was my extensive record keeping and ability to almost disengage emotionally in order to focus on facts (which wasn't easy, believe me) that provided info to new doctors right there during the visit. That helped them tie things together and find a very rare condition that mimicked heart failure - so my husband was sent to the right kind of specialist in a totally different discipline. So whoever goes along should not be so wrapped up in the emotional aspect of this that he or she can't be objective (and I totally get that it's highly stressful and worrisome and frustrating).
One of the things that was so hard for me in the depths of my depression was task completion. I could start things, but not finish. That left too many things undone, and that was another cause of stress. You might look to preparing small meals that can be frozen (to take away the cooking/shopping stress and even the "what's for dinner?" dilemma that can throw a depressed person into a tailspin. If you can get a little cleaning help or yard work help, whatever is left undone and making her upset, that can help. If she's stressing out about holidays, maybe you can do something to help. Take over Thanksgiving prep for her? Do labels on the computer for her Christmas cards? Then just tuck a card into each envelope, and maybe she can write one every 3 days, just holding them to mail a week or 2 before Christmas. If the grandson can make her a picture or a craft or just paint rocks to make a paperweight, sending that with an "I love you, Grandma" note can be a perfect little pick-me-up. Anything that creates a smile, even if it doesn't seem to perk her up more than that, can be a great thing.
I hope she gets in to see a good psychiatrist and that they find a good combination of medication and therapy, as well as rule out (or rule in) other factors that could be contributing.