Hi Karen
Ovarian Cancer Canada has this page on their website that explains more about what endometrial cancer is.
About Endometrial Cancers | Ovarian Cancer Canada https://share.google/M00TZrlb7tvOUzDtd
A very simple explanation that I use when telling people is it when the cells of the inner lining of the uterus (the ensometrium) become cancerous.
My understanding of adenomyosis (I thought I might of had this before my cancer diagnosis), is it is when endometrium cells found in the inner lining of the uterus are found growing in/into the outer muscle layer of the uterus. This page from The Endometriosis Network Canada (endometriosis is a whole other condition, where endometrium like tissue is found growing outside the uterus), has a good page explaining what adenomyosis is. Note - they do compare it to endometriosis, but I have found it to still be a good resource for myself when researching different things.
Adenomyosis vs. Endometriosis: What You Need To Know | The Endometriosis Network Canada https://share.google/FrkzlXIzxMOPDH6Ga
For me personally, they did not diagnosis my endometrial cancer from an ultrasound. I was diagnosed and continue to be monitored with an in office endometrial biopsy. I was 27 having my first one done last year, and that was the first gynecological procedure I have ever had done, apart from internal pelvic ultrasounds. It is similar to, or a bit more painful than an IUD insertion. I am not sure if you are asking for yourself or for your daughter, but depending on your gynecologist etc, if an endometrial biopsy is required, you should be able to ask to have it done under some sort of sedation if desired, etc.
Hopefully you find that helpful. If you have a gynecologist I would recommend speaking more with them about it. Take care, and wishing you all the best as you search for the answers you need.