Can the VA refuse to treat a 100% service-connected veteran citing their case as "too complex," and also refuse to outsource them for care?

No.

One of our Senators here in Oregon was having a town hall, and a veterna had complaints that the Senators staff had ignored his request for assistance. The Senator, Ron Wyden immediately asked his veterans representative that was in the town hall, and she confirmed that she had seen the complaint. The Senator fired the staffer on the spot. You state has 2 Senators, and you also have a Representative. Contact all of them in writing, put a CC line at the bottom of each with who else is also getting a copy. Send them Certified, so they can not say they weren't recieved. Also add the President to the CC. All of the out of pocket should be reimbursed to you.

I am happy to be retired and have medicare and BC&BS supplemental insurance. I have used such resources in the past to get a second opinion. I believe in covering my bases even if it will cost more outside the VA.

What VA hospital are you going to? The one in Fayetteville Arkansas referred me outside for a lumbar surgery and they covered everything. It just makes no sense especially if you’re back problem is service-connected

White House hotline # is: [login to see] . Call that number and explain your situation. It's a recorded line but you leave your information and they call you back to confirm the details, then make the appropriate phone calls.

The White House actually has a hotline for this type of fuckery. [login to see]

have you tried contacting Senator Tammy Duckworth's office?
as a Disabled Veteran, she'd probably be really interested in getting a fellow female veteran the Medical care she needs

I would recommend that you consult with a VSO (veteran service officer) if you haven’t already done so. These officers can be found through your local VA office, local VFW, American Legion, AmVets and DAV. These organizations are usually very good about trying to get the resources you need.
If none of these organizations are helpful, you can always direct your situation to the Va IG office.
I have had the same luck as you had concerning a Senator. However, this is an election year and It might ignite a flame under the ass of your congressman and Senator.
Since you are rated at 100% you should not be turned away for any illness or conditions that you may have. Service connected or not.
The Choice Program, Mission Act, Community Care or whatever that program is called now were designed for Veterans to get local care, especially if your VA doesn’t have the facilities to treat you. You could also be sent to a VA facility that might have the proper medical personnel and equipment to diagnose and treat you. At no expense to you. This also applies to all Veterans that are registered with the VA regardless of disability rating.
I’m sorry that I couldn’t provide you with much advice but I hope that this helps you.
God bless and good luck

Someone needs to listen to her. I don't have any answers. I wish you well.

It troubles me deeply that Veterans must FIGHT for fair treatment, butt, if you WANT a sex change ... JUST ASK !