Treatment and side effect of ca stomach

My sister is having ca stomach at stage 4 and it spread to pancreas, liver and ovary and she already took 3 dose of chemotherapy since 3 month and she is recovering well so far. Chemotherapy is getting very hard on her and taking all her energy out and she is having so much vomiting and diarrhea after chemotherapy dose. Now she is tired of getting chemotherapy dose and she want to skip one dose of chemotherapy.                         I want to know that it is ok to skip 1 dose of chemotherapy and I am afraid that by skiping the dose of chemotherapy, the cancer will get worse or not. Can anbody suggest me on this situation or anybody have suggestion for me..