splitting profit between investors

I have been in fashion business for about 6 years and I really want to expand my business and luckily I found an investor in my sister, but I don't know how the sharing formula will be in the long run of the business, I will be doing all the work from marketing, purchasing of the goods and the sells ,I will be fully in it because that's all I have and she will only be investing her fund of about the same amount that my business worth. So please what should be the right sharing formula of the profit.
Also I will be reinvesting my own profit back to the business as time goes on. Should the sharing formula be constant as time goes on or should it decline ?