If you are packing a marrow, and she’s had a lot of work, I can see why she might want a break - you wouldn’t want to running on a blister would you? Fanny’s get sore from lots of shagging, especially if a lot of it doesn’t stimulate natural lubrication, and they are just enduring it with no real stimulation.
I see guys complain that girls don’t like having their nipples played with/sucked, or complain that oral is too rough. These are sensitive areas over stimulated by excessive volume of attention. Treat them the way you want your bellend treated right after popping, and you’ll get better reactions as a rule.
She could have used any excuse really, she just sounds like she’s been fucked raw and doesn’t think your cash is worth the pain of you stretching her out right now.
If you accept it with good grace, you might be able to turn it to your advantage next booking- discount, free extras? Just a thought.