Just the intercourse??? yikes! No wonder she goes dry. That is way too long to go without lube. You aren't running a marathon!
So she's upset if she goes dry, you're upset if you go soft... Seriously, it sounds like you guys are putting too much pressure on yourselves.
I remember reading a survey once that asked men and women about how long the ideal length of time intercourse should be and while I don't remember the actual numbers any more, one point they made was that pretty much across the board both men and women assumed the other
sex though it should last longer yet what they actually wanted it to be was pretty much on par. Anyway, it sounds to me like you two might be suffering from the assumption that you have to go on forever just to please the partner.
As for the lube, if you use it as part of the foreplay and have some fun with it instead of waiting until she's actually gone dry, it won't seem like you're using it because she's 'failed'.