Can I assign my contract to multiple investors?

[Matthew Teuschel]

I have an assignment of contract signed with an investor to buy my deal. The problem is she takes forever to get back to me on the smallest things and keeps dragging her feet on setting up due diligence. 

My question is: Because she hasn't paid me for the deal yet, am I able to still market my deal to other investors and sign an assignment contract with them as well, and whoever closes first gets the deal?

I don't want to wait 3 weeks for this lady to find out she doesn't want the deal for whatever reason and then have to start all over with another investor. I appreciate any advice.