I am a graphic designer and i am trying to explain to a client why she has to send me the pictures in jpg.?

ok. i found this gig of laying and designing a math book using Indesign software. i need to prepare it and send to print for this teacher. she sends me every component as a word document. including the pictures and vectors. i have been working for years as a graphic designer and i know for a fact that the pictures she has sent me are way to small. to increase the size of some of them i have to increase them to a 200%. altough most of them do not exceed 4 inches wide and tall, there are 2 hundred of them and the document will be too heavy for In design, if i dont call the pictures through the software. i keep on telling her she needs to send them to me as a jpg or tiff format. still she questions to me why. how can i explian to someone who knows squat about design that she needs to send them to me on those formats??