Following with similar inquiry. I was diagnosed with MGUS shortly after my first vaccine (J&J in 3/2021). (I continued to get two boosters (J&J and Moderna) afterwards anyway but there were no MGUS flairups, fortunately.) Thank you for posting psue4. Looking forward to viewing other replies.

Greetings, nothing I have read on MGUS connects dots between the COVID vaccines and MGUS. I’ll probably never know exactly how or why I have it. There are so many common exposures that we think nothing about but are later informed are carcinogens. Tobacco exposure was at one time held harmless.
As Ginger says, MGUS is a wait and see thing. I found a good hematologist/oncologist and he watches for progression. In the unlikely event that my numbers get wanky enough that I require treatment, I will get a second opinion at one of highly specialized Multiple Myeloma treatment facilities. Until then, I feel fine. I go about my life not giving much thought to the MGUS. I travel, spend time with friends and family and enjoy life. I hope your daughter can do the same.
My one piece of advice, which I don’t think my fellow posters will find objectionable is to find the most experienced hematologist/oncologist that you can to monitor her blood work. That’s key. If you are getting surgery on a knee, you don’t go to a dermatologist. You want someone who is an experienced specialist.
Let us know how it goes.
Patty