Well, you know what to do then. Call her bluff. I bet she ends up leaving them, and If she takes them it's no great loss, you'd only end up changing them sooner or later anyway.
This is exactly what I did. Most of the windows have horizontal slatted blinds which are bespoke to those actual openings, in one case there are 5 blinds around a bay window at the front - the chances that they can be reused elsewhere or have any monetary value realistically outside of that house are nil. It's just extra hassle for her to remove them all, put them in bin bags somewhere, and let them rot in a garage for all eternity if she really goes ahead with this. She's moving in with her partner so it's not like she needs curtains and blinds for another property even.+1
The same thing happened to us and we refused to pay.
They left them anyway and it wasn't long before we changed them.
Call her bluff.
What are the chances they will match the decor or windows at her new place?
Her taste is not ours and we would definitely replace the curtains, blinds are somewhat innocuous and we'd retain them indefinitely, but we've got a baby under 1 year old and so will need to put up some kind of window covering so he can sleep the first night there - really didn't want the hassle of DIY on moving day as we're moving to a different county, not round the corner and also have a dog to move.
I have also sent the message back that when all these items are removed, everything needs to be made good including screw holes to maintain the standard of presentation the purchase price was originally agreed on... And she also tried to leave us her old washing machine when she changed the forms so I caught that and ask it be removed.
She's also removing every light fitting she can.
It's gone from a really amicable, easy transaction to her acting like a bit of a greedy twonk.
Anyway, rant over... see if she'll be pigheaded about it now!