Be more specific about how it dies, please. Does the engine kick out but the electrical system continue to function? (Does the starter still crank?) How old is the alternator?

Has any fuel line related work/maintenance been done prior to the first incidence of the problem (fuel pumps, fuel filter, etc.)?

Are there other symptoms/factors your sister can relate? (And what did the German car so-called experts check-out for that $1,800 she dropped?)

I have the same car and have never experienced anything remotely like your sister's recurring nightmare.

Please, keep us apprised!

__________________
Eric

1991 560SEL-Euro (185,000 miles)
1989 420SEL (Retired from daily use at 325,000 miles; Use as donor vehicle)