Legal Question in Wills and Trusts in Illinois

It doesn't necessarily make the entire will invalid, but the attempted changes may not be valid. Wills (and changes to them by way of a 'codicil') require certain formalities. That is, a will or codicil must be witnessed as required by statute. That means 2 witnesses who see the testator sign and who also sign as witnesses.

Unless the revisions/notes were properly witnessed, they would likely not be valid, and would also likely cause possible costly litigation. Your mom would be well advised to talk to an attorney about doing a new 'clean' will to reflect her current wishes.

Without actually seeing the Will, it is difficult (or perhaps, impossible) for an attorney to adequately answer your question.

However, if she made handwritten changes to her previously signed Will, there are one of two likely results: (1) the Will has been revoked, or (2) the changes that she made to the Will shall be entirely disregarded, and the terms of the 90's Will shall remain in effect. In either event, she should consult with a lawyer who can provide her with a new Will that has been signed, dated, and witnessed appropriately. Most attorneys, including me, offer free consultations for something like this. Since you personally might benefit from changes to your mother's Will, you should absolutely not attend meetings with your mother's lawyer or participate in the drafting of a new Will in any way whatsoever. Simply provide your mother with the contact information of an attorney, and encourage her to see that attorney to address these issues.

Your mother needs to talk to an attorney. You are apparently more worried about the validity of her will than she is, which means some family buttons need to be pressed.