My Mom's making some incredibly bad financial decisions. Can we have her declared incompetent?

Bad judgement is not necessarily incompetence.

Declaring someone incompetent, if in fact they are incompetent, costs between $7000-$10,000. Talk to your mom and find out what's going on. It's free. ;-)

FIRST and foremost, hired an Elder Attorney, specializing in elder care. Find a reputable and compassionate EA that will treat your mother with dignity. YES you could be declared "guardians" and it sounds like you need to contact one ASAP. It borders on "elder abuse" when parent's can no longer fend for themselves, take care of their home, don't eat correctly, clothes are dirty, yard is overgrown, financial matters are left unattended, etc.
Call the elder attorney ASAP and set up an appt. either with or without your Mother to explain circumstances....I don't anything about $7,000 to $10,000 ? or where that figures comes from.....if your Mom is ill, with dementia or Alzheimer's she CANNOT speak on her own...many agencies out there to help....

That one event does not sound like it would be enough to determine incompetence in and of itself. You need to step back and assess how they are handling other bills and other tasks of taking care of themselves.

I realize those with Alzheimers do make bad decisions. The only credit card my husband has is a Walmart card, and it is used only for gas. My husband does drive still, and so far has not used it otherwise.
I took his other crdit cards and I hid the checkbook. So far so good..I throw away all that junk mail, altho it is important to him to see it. But later in the night I go to his office and throw away all except an insignificant letter or request that I am sure he won't answer or question. There are many requests for money. And the phone calls are exasperating. I requested to be on the no call list, but he is still getting calls. He is getting better about not answering unless he knows the caller. marymember

marymember,
if you ever get your hands on that little dog making those calls, please contact me. i promised to rip off her head and i havent given up hope yet.

Cherienels could it be she sold at a low price to avoid the headaches/effort/stress of having the house on the market longer? It is hard to even judge if that was an "incredibly bad financial decision" and with no other examples it is hard to guess if she is, indeed, incompetent. Does Mom have dementia or some other cognitive disorder?

Is a doctor involved in Mom's care? Are there doctors willing to declare that she is no longer able to act in her own best interest? Having her declared incompetent and a guardian appointed for her requires court action. (That is where the costs come in.)

As others have said, making poor decisions, or decisions one's children don't approve of, is not in itself "incompetence."

AgingCare has a few dozen articles about incompetency and guardianship. This one is a good place to start: https://www.agingcare.com/articles/how-to-get-guardianship-of-elderly-parents-140693.htm

Is your mother no longer competent to make decisions about your dad's care? Do you think that he needs a guardian, too?

Research in your area - find a reputable and compassionate ELDER ATTORNEY for your Mom/Loved One. Their advice is invaluable - and makes the caregiver accountable to the loved ones attorney. Caregivers, and that includes myself many years, should be held accountable for EVERY cent of loved ones resources.
My top piece of advice in my book: Hire an ELDER ATTORNEY that specializes in elder law for your loved one.