Hi @smithmom ,
What happens if you leave the charger connected and on? Does the tablet stay on then?
If so the battery may be failing to hold its' charge. How old is it? Even rechargeable batteries have a lifespan.
If it is determined that the battery is the problem, here is a link to the ifixit guide on how to replace the battery in your tablet.
Here are some links to suppliers of a suitable replacement battery for your tablet.
These are not recommendations to use either of them, they are shown to give an idea of the price of the replacement part. There may be others online that suit you better.