Hi mzkobus and thanks for your post. While we cannot provide medical advice or diagnostics over the internet (for your own safety), your concern certainly warrants a comment. I'm sorry to hear what your Mom (and you) are going through.
In the most general of terms, an oxygen saturation of 21% is a critically low number. You may want to get the information about what this oxygen level means by speaking with the physicians providing care to your mom.
Please do check back and let us know how she (and you) are doing.
All the best, Leon (site moderator)