[] Pleb test on a seed you haven't interacted with yet: Figure out if this is an inherent property of enchanted grief, or did you transferring your magic during your experiments on clear seeds transfer your power.
A subsequent vote, if it's confirmed:
[] Could you do something similar with teaching magical girls? Experiment with channeling your magic into Mami's her ribbons. (Hold off on anything more direct than that until you're more consistent in not breaking things when you enchant them.)
-[]Possible alternate solution: Recall your examination of Sayaka's power gems: How would you go about constructing one manually?
[] Ask Mami: When you channel magic into her ribbons are you extending your powers? Or is she holding onto some small portion of your powers when you do that? You want to see if you can share your memories of the times your were most in tune with your wish, how they relate to her own feelings about herself, and see if you can share a bit of your wish, and your power, with her that way.
--[] Ask her to tell you if she gets a headache or anything, as that's probably a sign that you should stop and try again later.
-[] Channel into a ribbon the times you were most in tune with your wish, and where it intersects with Mami's own feelings and her pride in herself. Talk as you do so, and let your words give context to the feelings.
Sympathy and Unity (entrust yourself to someone else, you will never be alone)
--[] Be careful. Go slowly. Take your time. Don't rush. Enjoy the moment and treat as a quiet conversation you're having with your magic just as much as you're conducting an experiment together. If you need to abort the test just enjoy it with words instead of magic.
List of Emotions Begins here:
--[] The times you've saved people and helped them be well, and Mami's pride in aiding others: Pulling Sayaka and her family out of the fire. Masami and Hiroko, Touhoku and Sendai's reaction after you gave them the clear seed. Contacting Kazumi and bringing her over. The many people you've saved from witch kisses.
--[] The times you've helped magical girls to live and work together, and Mami's desire to have others in her life: Helping Homura work with others. The times you've fought witches alongside each other. Assisting the Saints. Shopping together. The Picnic. Karaoke.
--[] Your powers, discovering them, learning, teaching. The times Mami spent advancing her own magic, and in being a teacher of others: Being a mentor to Sayaka, the comments on how far she's come, and your hopes for how far she'll go. Your troubles with enchantment, her tale about first making her muskets, how it felt when you first succeeded, and the feeling of enchanting grief. The times you spent learning from Mami and she spent teaching you. The first time you cleansed Mami, and the amazement she felt. How it feels to cleanse and the relief that's felt afterwards.
---[] Here and now, sharing this with her in hopes that something
amazing can come of it.
(alternatively, the same could be done for Homura, if altered to fit.)
[] Give her an enchanted grief marble while you work: see if she can do anything with it, personally or with her ribbon.