Yes, one of mine is very similar.
My sister was doing some small things, more hobby based, started to branch out into online. I wasnt working (just had baby) and was looking into options to keep me busy and asked her if she would consider letting me in on her business.
Best thing we ever did:). In our case it has worked very well. Having two of us has helped it to grow. I think the biggest thing for us is we both have strengths in different areas, we rarely have any crossover. We don't have the same roles in the business, and we respect each others roles and opinions on our sections. Also if she does something I am not 100% kosher on I usually back down, as it was her business in the first place, and without her input I couldn't do my side
We also live 5 hrs apart. With email and phone it is easy to keep up to date, we send millions of emails a day so each one knows what the other is up to. When she goes on holidays, I take on her role, and when I go, she takes on mine.
If one of us is having a rough time of it, the other steps in and takes over for a bit.
So for us, it works excellent, we have a good relationship. We have been doing ours for a few years now. But in saying all that, most partnerships fail, even if they are family. So I would think long and hard about it.
You need to consider all possibilities as well, like if you had a disagreement what happens? If she wants to quit, or you want to quit? How you are going to split money and costs? What happens if either of you get sick, have more children etc. Think lots of worst case scenarios and how you think you both will handle it.
It may even be worth getting agreements made up, if you are using BIL's and DH's etc in case there are any disagreements if you are both working in same area, ie it is your ideas, but they will be producing them. I would even consider protecting your idea yourself with design registration.