With Local Extension Like you discuss it is not really Linitis Plasitica which is usually confined to the the wall of the stomach and makes the tissue "more rigid, less flexible" as the name implies.
She should have chemo Radiation and then possibly reconsider surgery if she has a good Response. The treatments are rougher on the patient since the stomach has to be treated and she should probabley be set up for enteral feedings and given regular antiemetics before chemo and the radiation treatments.
Linitis Plastica usually doe better if surgically removed because it is sometimes more localized.