… los ingleses, unos a modo de salteadores de caminos,

… los ingleses, unos a modo de salteadores de caminos, querían cogérsela para sí. - some in the manner of highway robbers, wanted to stick it to her??? Is this right?

Coger is take, grab, seize. They wanted to take (coger) something (la) from someone (se) for themselves (para sí)

Ahh, gracias Francisco - de nuevo!

“Coger” is a tricky word in modern-day Spanish because, while it does mean just “take” and is thus used by many people, either on its own or as part of set expressions, it also has developed a sexual connotation (akin to the f-word) in some Spanish-speaking countries. Not here, in Spain, for example, where it’s a very usual, neutral word, as in the text you’re reading.