The original question is ambiguous. We don't know whether the company is underperforming what it predicted at time of investment or whether it is "merely" underperforming what the investor expects.
However, one thing is clear, the expectations of the company and investor are now not consistent. The company is expecting more help and the investor is expecting more sales.
It's a bit of a red flag when the company talks about "unwritten principle" wrt investor help. Did the investor agree to that BEFORE investment? (When you take "smart money", you get explicit agreement on both the "smart" and the "money".)
It's also unclear what the company means by "burning bridges". What, exactly, are you considering? The right answer is "we're going to keep our investors informed, ask for help, and work like crazy". Note how that doesn't depend on how the investor feels or acts....