The day you propose will be a day she remembers and cherishes forever. Sometimes your proposal happens in a way that she may not be at her prime, maybe it takes place while she’s in her Pajamas, or while you are camping, if that’s your thing.
Think about if she would want to be dressed to impress that day cause maybe you could have that arranged. She will never forget this day so, a lot of ladies would want to be looking stellar, which she probably always does in your eyes.
Depending on what your plan is you may have an activity lined up where she will be dressed her best anyway, or you could find a way to get her to dress up.
After you propose she is going to be wearing the most important jewellery she will ever wear. She’s going to be showing all her friends and family, wouldn’t it be nice if you had managed to get her a manicure before that day so she feels even better showing it off. Get one of her friends to take her out. Or treat her to a spa day. Not every women would want a manicure but, if you think she might, it’s another detail you can add to the big picture.