Hi Nansoval!
Wow! So your mother is almost 94! I would love to have had mine live that long! I hope you and your sister appreciate the gift of having her this long, especially since she is comfortable and so forth. Not saying you don't, just saying I think the joy of that should be first and foremost.
I'm not sure why you're ashamed of how she dresses? Are her clothes worn out and often dirty? Or is it just that she doesn't buy/wear the latest styles or that she opts for less expensive ones? If it's the condition of her clothes that you're worried about, I'm totally with you there and think you should try some of the suggestions others have made.
If it's just the style or the low cost, then, I'm sorry but I don't think that's up to you or your sister. In fact, Mum may argue with you over it cuz she feels you're treading on her independence. Some elderly people, I know, feel that one of the perks of aging is that they don't have to worry about being in style and stuff, anymore. You may not agree, but I'm sure you can see that she has a right to her own opinion on that subject. And that just cuz she's old doesn't mean she doesn't have a right to make her own decisions about how she dresses or anything else.
You can't help how you feel, but please - pick your battles with Mum. Cuz I hate to say it but you don't know how much longer you'll have her.