My 84-year-old mother changed her will at the last second, leaving her entire $1.2 million estate to my sister. How can I challenge it?

Let’s say, for example, that Isla is upset because her mother Marion adjusted her will at the last minute. Marion died at 84, and she’d changed her will about two weeks before passing. The updated will left Marion’s entire $1.2 million estate to Isla’s sister, Piper, and Isla suspects Piper convinced Marion to change the planned split.

Now, Isla is trying to figure out what to do. She wants to know how to challenge Marion’s will, but experts say things aren’t that simple.

Isla likely has a right to contest the will

First things first. Isla can only challenge Marion’s will if she has standing, or a personal stake in the case and the potential to be directly harmed by the situation.

The good news for Isla is that she likely does have standing, according to Evan H. Farr, a certified elder law attorney.

“Standing typically belongs to another child who would have inherited under an earlier version of the will or under the state’s intestacy laws,” Farr told Moneywise.

However, Farr warned that “the time for will contests often is short,” and Isla needs to act quickly to find an attorney and start the process.

“You will need to file a contest in time in order to preserve your rights under an earlier will,” he explained.

Isla must be able to prove there is a problem

While Isla likely has standing to challenge the will, she also needs to have grounds, or a solid legal argument, that the will shouldn’t be considered valid. Simply not liking what the will said doesn’t give Isla a solid legal argument, nor does the fact that her mom was old and the change happened late in life.

“Your mother’s age and the timing of this change do not automatically invalidate her will,” Farr said. “Someone with sufficient capacity who acts voluntarily can change their estate plan at any time prior to their death.”

As Amanda Butler Schley, a business attorney and founder of Business Law Group, told Moneywise, Isla could successfully challenge her mother’s will “if her mother lacked the mental capacity to make the change or was under undue influence when she changed the will, and [there is] a way to prove it.”

Fraud, forgery or failure to follow the formal requirements for a will could also support a successful challenge, but Isla needs evidence of these issues.

“Isolation, control of the decedent by others, communications with the drafting attorney by the sister and a sudden change in the will that is very favorable to the sister all indicate possible undue influence,” Farr said. “However, helping a parent with their affairs or setting up an appointment with an attorney for the parent doesn’t, in itself, prove undue influence.”