Not sure why you have such a strong opinion when the following fits into the story perfectly:

- She's had rape type play with other partners in the past and didn't understand why he's stopping when she says stop.

- May not have had any talks about it with prior partners and had no problems with them.

- Sees her partner confused and freaked out about the situation.

- Was already not very equipped to talk about kinks as shown by it not being brought up ever and now she has the added partner freaking out making it harder to talk about.

Physical or mental trauma are obviously possible but you're basically discounting something that is clearly very possible and it's completely reasonable to believe that a kink is more likely.