I've got a customer who just doesn't speak to me, ever.
a complete door handle if you ask me but there you are!!
I've had one like that; it was her daughter who asked me to quote for her Mother and organised it all. Her Mother was ALWAYS in and when I knocked for payment the door would open a fraction, and this bone-white chubby hand used to pay me; always in the correct money - no need for change.
Then the door would shut! I never saw what was on the end of the hand; thankfully.
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But if a customer hasn't the social skills or the tact to explain properly why she/he can't pay when I'm there, I'd seriously consider dropping them. I've done this since I started and I'm chuffed to say that on the whole I've got a nice bunch of customers.
I'd consider how long she's been a customer and what her 'previous' is for how she's treated you.
She's probably just hormonal, tired, and skint. Babies aren't cheap!