How to obtain a multiple-entry Schengen visa from the USA for a Russian citizen?

A Russian citizen, permanent resident of the US, lives in the US and travels to Russia 3-4 times a year for about a week or two. Since most convenient flights for her habe an intermediate stop in Europe (e.g. Frankfurt, Helsinki, Paris, Milan, Reykjavik) she would like to exit the transit area of the airport and spend a day or two in the country of transit.

At present, she applied and received multiple short-term Schengen visas from Finland, Sweden, Iceland, France and Germany (about 5 total). However, despite her requests the visa was always granted in the C-1 category (30 days validity) single or double-entry. The visa process is very time-consuming (collecting all the paperwork) and has to be planned many months in advance (waiting line for German consulate is 1.5 months as of today). She, to the best of my knowledge, has always complied with the visa requirements, has a reasonably well paying job (>$100K) and some property in the US. However, each and every time the visa granted is C-1 with 1 month validity and with the duration of stay for tje exact duration of transit +1 day.

Why? What is the secret to obtaining a multiple-entry Schengen visa with at least half a year validity?

It turned out that receiving a MEV does not mean it is in any way a long-term one. The next visa received is a MEV, but for the exact duration of the trip: 14 days.

The current table for Schengen states US consulates, sorted by % of MEVs given per consulate:

PS. This question partially overlaps with this one. However, the forms were always filled requesting multiple entries, so the answer provided in the linked question is not sufficient.