So write something, there are lots of websites that show you examples of rerefence letters and ask your previous employers to sign.
Make it up yourself, very doubtful anybody from here will or can check up on one issued from US, especially if the contact details are not quite right on the letterhead......
She works as a personnal trainer/yoga instructor, very much a hands onm business, within 1 week the employer will know if she is any good or not.
I didn't say to lie about what you write about yourself, just make the rather irrelevant certificate up yourself
Or if you can not get those letters simply list the previous jobs in your resume, and maybe the contact details of former manger(s) (after asking the person if o.k. to share these details).
I worked most my life in the US and something like this is just not a thing. US corporate policy is that if requested they may, give you a two sentence statement that you worked at their company, but it is not a requirement.
As such, I have a couple of reference letters and one confirmation statement. For all other companies I worked at I can literally not get them. A couple of them do no longer exist or they do not answer my repeated request for a statement.
Very frustrating encountering such arcane HR practices...not to speak of the personal info You have to put on the CV...