I used to work in VC and have seen a few examples of this. Every case is a little different, but from what you've described I'd focus on salvaging the co-founder relationship. Conflict like this is totally normal. IMO, a pivot is when you change directions based on new information. It sounds like you're not pivoting, but lost. If you haven't already, addressing this head-on and having a candid conversation about being lost would be beneficial. Think of it as an exercise to possibly strengthen your relationship via conflict. Few other thoughts:
1. At this early stage of the business, the core asset is really the co-founding team and their relationship. Conflict is very much normal, but how you resolve it is important. You should be able to articulate your co-founder's concerns. For ex. she might feel the pressure to show "progress" to your investors.
2. It takes a lot of time and energy to build a good working relationship. Moving onto something else might seem like a good idea at the moment, but you could be right back with the same issue with another co-founder.
3. If you do decide to move on, end the relationship as amicably as you can. Note that this is not necessarily the "quickest" route, but it'll help keep your reputation intact.
Edit: spelling.