What to do when a 90 year old has a pancreas blockage by a cyst? Are there treatment options that are not aggressive?

A close family member had this. He was young so it is likely a very different story for older people. The doctor did suggest surgery which would have been very invasive with lasting repercussions so we asked if there were an alternative. The doctor suggested he go on a virtually no fats diet to see if the cyst would shrink. He did and It did and after a year it was no longer detectable. He can eat fats now but in limited amounts (he had a flare up a when he was not watching his intake). The Doctor told us the cyst itself was not not a precursor to cancer but if the duct becomes blocked the pancreas becomes inflamed which can cause damage that would predispose him to cancer (complicated I know).
Anyway I am not a medical professional and I am NOT suggesting you not do surgery nor am I recommending any kind of diet change. Only a doctor can prescribe action or treatment. I'm just telling you my experience.

If a cyst is blocking a duct there is no answer but it has to go.
Pancreatitis can be dreadfully painful.
There is one hospital in San Francisco--and only one--that I know of about 8 years ago (so more now??) that does non-invasive surgery through endoscopy in the area of gallbladder, pancreas and common bile ducts connecting. At the time my step daughter had such a surgery when she was in a debilitated state from another condition and could not tolerate surgery and had a stone blocking a duct between pancreas and other organs and a consequent pancreatitis. At that time she had been transferred from Kaiser for this surgery; we were told that this surgery technique was being taught. That hospital was California Pacific Medical Center, or CPMC. I have otherwise no knowledge and don't know if this technique is now more commonly done or not. The surgeon where you are may have more information for you?
You might try to use google or other search engines to look up "Non-invasive surgery on pancreas or gallbladder" and see what you come up with. My step daughter at the time had mild sedation and the surgery was VERY minimally invasive or disruptive; included basketing out a stone and putting in a stent in the duct.
Between the doctors and the internet I hope you can learn more. Do also know that they can often do surgery through tiny scope now with virtually two small punch holes for access of instruments and light; but again, bigger the hospital the more likely to have these "cutting edge techniques" for treatment.

Quality of life, above everything else. Ask any doctors directly involved in her care for her odds, treatment options, and potential consequences.

Ask her what SHE WANTS. If she’s unable to comprehend her situation, YOU will have the peace of knowing that you at least attempted to involve her in the decision.

I placed MY Angel mother in a very good residential facility, and she lived 5 happy comfortable, safe, and well cared for years there.

You may find yourself in a situation in which there will be NO GOOD CHOICES, so prepare yourself in case you need to choose from a selection of less than perfect choices.

My gut if she were mine would be to give her a little more time so that I could explore potential different treatments.

Hoping for the very best for you both.

How is her health otherwise? If she's not on her last leg, I'd at least look at options, especially the more natural, less invasive type. Google it, talk to her doc, etc. Is she still competent enough to decide if she wants to purse treatment? Some people are content to just let nature take it's course, especially at such an advanced age.

I am not a medical expert so I won’t even attempt to answer.

There are nurses on the forum. Stick around for answers from someone who has experience in this matter.

Have you spoken to the doctor since this occurred? Do you think you need to make an ER trip to the nearest hospital?

Best wishes to you and your mom.