The raspberry leaves are meant to add magnesium to their diet, but if they are very low in magnesium I have found they don't do much. The powder is more effective. I feel when they are cycling they tend to be lower in magnesium, though that is only my observation and not scientific in any way.
Also another way to look at this is that she doesn't need to learn to go out with out Rocko but that you can honor her wish of having him join her. It's not a battle for us to win against them, but it can be a time for us to learn to listen and then respond accordingly. If she is feeling lots of angst about leaving him and you keep making her leave him it's very likely that feeling will actually grow and get worse and not get better. Horses really respond to us when we listen to them. Just another way to look at the situation.
My mare Sky was so anxious when I would take Zorro last year. She started to become a danger to herself (and us!) and would race around smashing into fences and gates and falling down on the ground. This started with her whinnying and running around when I would take him out and escalated to her hurting herself. I finally decided I would just take her everywhere with us. So for about 6 months I did that. I have found that now I can take Zorro on a drive or even drive away in the horse trailer and she will whinny but doesn't run around, panic, pace or worry. She just simply goes back to eating. Is this because I honored her worry and allowed her to join us and she found it's easier to stay home? LOL! I don't know exactly and wish I could just simply ask her. But for whatever reason, she is calm now when I take Zorro away.