My dad died and left most of his estate to me. His ex-girlfriend got $200K from his 401(k) — but now wants a share of his pension, home. Does she have standing to challenge the trust?

You'll unfortunately need to decide how to respond and whether she has grounds to contest your dad's plans. In this case, she wouldn’t be able to challenge the trust — unless she had a valid reason for suddenly expecting more of his assets.

Here's what you need to know to cope with this conflict and honor your father's legacy.

Does she have legal standing?

The good news for you is that your dad has provided clear instructions and his estate plan seems solid — but you need to understand how his plans affect his ex's rights and your responsibilities.

According to the U.S. Office of Personnel Management, when someone leaves behind a pension, they typically must name a beneficiary who collects any benefits available after their death. If they're married, the beneficiary usually must be their spouse unless their spouse signs a waiver giving up their rights.

Your dad's ex-girlfriend wasn't his spouse, though, so she may have no legal claim to the money if she wasn't named as the designated beneficiary. The pension must be distributed to the person your dad selected.

Your dad likely also provided instructions in his estate plan for who should inherit his home and, when he created the trust, would have included specific details about how he wanted assets to be distributed.

If you're administering his trust, you must follow his written instructions as you have a fiduciary duty to beneficiaries, according to Boston law firm Choate, Hall & Stewart LLP. Unless the trust says some assets should be given to his ex, you can’t distribute trust assets to her.

Now, the ex-girlfriend could try to contest the beneficiary designation on his pension and could try to contest the trust by going to court.

However, she would need standing or grounds to do so. You have standing only if you'd be likely to be named as a beneficiary if something hadn't gone wrong. People with standing usually include family members and other estate beneficiaries.

Because the ex-girlfriend received some money from your dad, she might be able to make an argument that she has standing to contest the estate plans put in place. However, even if she's allowed to challenge his plans, she still must convince the court there was a problem.

For example, she would have to prove that your dad wanted her to be the beneficiary of the pension, home and trust assets but did not name her as the beneficiary because of fraud, duress, forgery or incapacity at the time the estate plan was created.

Assuming your dad provided clear instructions in multiple documents (including his beneficiary designation and the trust documents) while leaving her money elsewhere, it's unlikely his ex will be able to prove that fraud, duress or other problems led to your dad's choices. This would mean her challenge most likely wouldn't be successful.

Still, since you may find yourself facing legal issues, it's best to talk with an estate planning lawyer about how to respond. Rather than giving her money to avoid conflict — just make sure you’re prepared with professional help if she tries to fight the trust.

The importance of estate planning

In this scenario, your dad did everything right, as he left behind instructions. Far too many people don't. In fact, LegalZoom reports that only 33% of U.S. adults have estate planning documents in place.