It shouldn't be a problem as Direct relatives of US citizens including parents are generally forgiven for overstay as long as they have no criminal history. It is very important that she does NOT leave the USA whilst the adjustment of status is proceeding as she will not be allowed to re enter for 10 years. No travel until Green card in hand!
There are a number of threads here that discuss this situation if you do a search.
Good Luck
There are a number of threads here that discuss this situation if you do a search.
Good Luck