There could be any number of reasons she didn't raise the child herself and left him with her parents.
Have you looked for a marriage? She may have started afresh and had a family with her husband.
The 1911 census gives the number of children still living so if you can find that census for her parents it would indicate if she was still alive or not.
Looks as if Albert and Mary Jane both died in 1908 though Mary Jane seems to be Jane in census. Ages in census and death registrations are very inconsistent. As Mary Jane/Jane is recorded as born in Ireland I'm tempted to say that's an avenue to explore for Mary A in later years.
I knew I had seen number of children born/alive somewhere.
Mary Jane is all over the place, claiming different birth cities, countries and years on every census. She was a big drinker if the local news archives are to believed. She also doesn't appear on paper pre marriage which is something I'm also focused on, but am waiting on DNA results as I've explored every other avenue for her.
I'll do some searches for Ireland next, I don't think ancestry includes Ireland in the standard searches, so I may have missed something glaringly obvious.
Thank you