has she had a traumatic incident with the nail clippers???

Like was her quick actually cut when she had her nails trimmed once? This could be a result of a traumatic incident.

Suggestion: try not clipping the whole nail all at once try just barely taking anything off the tip (does this make since) try doing this while she's sleeping or just really relaxed...

Other thought

Try going to a pet store and buying a mild sedative. They're usually marketed as calm down, anxiety relief, or travel fomula's
Let me know if you need some suggestions on brands or where to find them online.