Has she elaborated in regards to the block that happens? It sounds like she has a bit more going on than I’ve experienced so it’s hard to say. In general though, it’s super common for there to be a mental block that causes a build up + fizzle out effect. It’s really easy for our minds to wander because that build up can take a while. She might start thinking like..why is her body taking so long to get there, are you getting bored or tired etc.. overall mentally distracted by really wanting her body to cooperate already. It’s frustrating! Two things I’ve found most helpful are finding ways to shorten that time prior to (more foreplay, teasing etc) and having a go-to arousing mental imagine to think of. For the second one, the moment I notice my mind thinking of anything other than the physical build up feeling, I cut it off and force myself to envision whatever I find arousing whether that be a particular act, image or usually video clips. It keeps my mind focused on feeling good and has made a huge difference. Maybe she would be open to trying that?