My sister has not showered in weeks. Any tips or ideas?

Introduce your brother to the wonder of no rinse products - for bathing and washing hair.   They're effective, easy to use, and  a  lot safer.

https://www.agingcare.com/search?term=no+rinse+products

There are a lot of posts at this link addressing the substitution of no rinse products for full immersion in the shower options.    Rehab facilities use them; they're far safer than immersion bathion.   I used them when I was hospitalized for a ruptured appendix.   I was surprised how refreshed I felt after cleansing.   I still use them periodically when I don't feel up to a full shower.

Liked the idea of the no rinse products. Also .... if you think she is afraid of falling in the shower, you might place a shower chair there for her. They are sturdy and can be warned up with a spray of warm water. I've been using them since I was 50 and had a horseback riding injury.

Honestly i have had this same situation so often repeated by any senior over say 70 years of age. They mainly don't want to feel cold. Which of course shouts to me that they are low in iron too. Many seniors don't physically move around indoors enough so of course they feel chilled. It helps to get them up and active doing something outside then let them know it would benefit them to shower when they get back home. Letting them know of the importance of hygiene & that water is good to shed off dry skin & accumulated clogged pores, ear wax build up & general odors etc. might help. Enthusiasm about the whole ordeal helps and grooming should be a set routine etc. Non- slip Bath mats & shower chairs have back support seats now that glide on rails to help one sit & get pushed from outside the tub to into the tub. I know since one of my clients had trouble with bowel incontinence & UTI's that the fire dept can be called to help if there is trouble getting someone from the toilet to the shower. It can be dangerous! SO the hand held shower line is very important for cleaning up. Otherwise, have grab bars installed so when an elder closes their eyes, they will feel secure on the chair & even if short standing is possible. While helping them if they have disability to reach themselves, the grab bars are best too. Standing at the kitchen sink is another alternative if they complain about getting so cold. Just to get their hair & head & face clean helps get them into the mood for hygiene.

Warming up everything helps: room, towels, shower water... It might also be time to pay for a female bathing assistant from home health agency to "help" with bathing and dressing every morning.

What a fine long-distance job you are doing.

Most caregivers are learning on the job - suffer stres & tiredness. Also have to adjust to a massive change to their marriage. A friendly phone call to support (& tips if they ask) is both practical & caring.

Pam, you have most everything from my list already!

Warm bathroom, towels & bathrobe in sight, water on & already warm. Calendar too. Shower days marked 3 X week is a good start. It keeps the routine (as too few & the routine can get lost, becomes in danger of 2, 1 then 0 again).

Hopefully having a routine will help, regardless of the reason; pride, fear, memory or sensory.

One last thing, which I am reluctant to even add, is medication for mood. This can help too. Knock a small edge off so many refusals.

You've made some good suggestions yourself and others have provided some more to try to tackle the showering. Definitely making the room warm, even like a sauna, which might help if it's only because she is cold. Often when visiting my mother in MC, most of the ladies would be bundled up, commenting that it was chilly in the place. I found it comfortable in winter, and in summer with the AC it wasn't too bad. I'm not a fan of cold, esp how some make it so cold with the AC. I arrived once VERY hot because of the heat and humidity outside, so I came in with jeans and a tank top (hoodie around my waist, for later.) Several of the women, including my mother, would ask me over and over "Aren't you cold?" Not yet! I had to wait for my temp to come down quite a bit before needing the hoodie. A stable shower chair might help as well - I've read comments about some that have a hole in the middle, to allow some cleaning of the private parts while still seated in the chair.

My mother also tended to "live by the calendar", at least in the early stages. Adding shower to the calendar one day a week might help - once a week might be okay, esp if he can handle clean ups between showers. Perhaps if she sees the reminder on there, it will make her more likely to agree, once the room is nice and toasty. If not, those no rinse products might take care of things.

If all else fails, perhaps he could try hiring someone to come once/week or once every two weeks who can encourage her to shower. Often there are postings that say how a LO won't shower for the family care-giver, but they will for the aides. Worth a try if nothing else works. If the one hired is good at it, they can often find the right words/methods to coax the person into the shower. It may take trying different people, giving each one a few shots at gaining trust and coaxing. Even in MC the staff has to work this out. They run into the same issues, but can't force anyone.

Changing clothes - does she change into nightwear before bed? If so, take the clothing for that day away, tuck into washer or laundry basket, somewhere that she won't see it and lay out new clothes for the next day. When my mother was still living alone in her place, my YB installed some cameras to monitor the doors, but the one at the front door could see a bit into her kitchen, where she generally sat at the table often. For a woman who had YEARS worth of "bargains", name brand stuff bought at discount, with enough clothing to open a store and also be able to wear something different every day, it was perplexing to see her in the same outfit, day after day. She would always relate how she got compliments on her "ensemble", with matching shoes, jewelry and purses. The items she was wearing were more run of the mill inexpensive stuff. Granted there were many items that no longer fit, but you'd have to have seen all the clothes she had, including still packed in her closet! One time she wore an outfit 6 days in a row! I often wear the same items, as I'm not working and don't get them dirty or smelly really, so they can be worn again and I'm not into fashion, etc., but for her that was not normal. When OB was visiting, he even pointed out food stains on something she was wearing for a second or third day in a row. She looked at it and laughed. It didn't bother me that she was not wearing her nicer things, just seemed odd for someone who was so "into" being in nice things.