People with depression tend to see everything in a negative light and sometimes loose the ability to think rationally. So argueing rationally isn't going to work.
From my experience, there are 2 ways to ensure they take their meds:
This is usually the case for inpatients in a mental health facility. A figure of authority (the doctor or nurse) tells them to take these pills and they are required to aktually take them. The patients don't have to like taking pills, they don't have to like their doctor, but they have to take the pills anyway.
Of course the times of patients being forced to take medication against their will are long gone. From a psychological point of view, though, it's easier to do something we're reluctant to do if a person of authority tells us to. And the doctors and nurses are trained to interact with people with severe depression.
You, as a friend, aren't in a position of authority. Probably even the family members of your friend don't have enough authority right now to make her take the meds. If the problem cannot be solved otherwise, institutionalizing your friend may be the best solution until the medication has evened out her symptoms enough for her to take the meds voluntarily and regularily.
As mentioned above, people with depression tend to see everything negatively, even those things that could help them. If your friend is in a bad mood and you say "please take your meds" you add to the bad mood because you indirectly tell her she made a mistake (forgetting her pills).
Instead, you should present her meds as something positive. No matter how she argues, always turn her argument into a positive outcome. Some examples are:
(She) You just want to blame me for being sad.
(You) There is no-one to blame. I just want you to feel happy again and you told me that your meds make you happier than you are now.
(She) You ignore how hard my life is.
(You) I don't ignore you. I see how hard it is for you right now. Your meds always made it easyer for you to cope with these difficulties, that's why I want you to take them. They'll help you.
(She) I don't want your advice.
(You) I know that you don't want my advice, but I also know that your meds make you feel better. You told me yourself, and as your friend I want you to feel better.
Unfortunately, there is no guarantee for success. When your friend is depressed, you cannot argue with rational arguments. Her brain works differently in those moments and sometimes it might seem like she is a completely different person. As soon as her brain calms down, she probably fells guilty of reacting that way, but in the spur of the moment she has no way to control herself.
The best you can do is stay strong and stay her friend. Being a loyal friend with someone in a difficult situation is much more beneficial than threatening to end this friendship ("take your meds or else..."). Maybe seeing her as a different person in her dark moods is a way to cope with it. You like your friend, but you don't have to like her when she's in a dark mood.
In case someone asks me how I know this or where I gor these experiences: I don't want to disclose this information.