CelticPrincess, well done your school for taking in the refugee children 
RC schools are voluntary aided schools, and provide collective RC worship (Mass, various prayer services) according to the policy of the RC bishops.
www.catholiceducation.org.uk/schools/religious-education/item/1002967-about-religious-education-in-catholic-schools
RE is part of the state mandated curriculum.
How much of the RE curriculum is given to the teaching of other religions?
The RECD does not prescribe how much of the curriculum ought to be devoted to the teaching of other religions, however it is clearly an expectation that it should happen in every key stage. In practice, most Catholic schools would spend approximately one half term per year on the teaching of religions other than Catholic Christianity. The requirement in the revised GCSE that 25% of the study should cover a second religion is not incompatible with this practice. This is because in Catholic schools the 10% of curriculum time which is given to RE is more than is required to teach a GCSE which is designed to be taught in fewer hours than this. The expectation has always been that this additional time which Catholic RE departments have is to be given to the supplementing of the GCSE syllabus in such a way as to allow it to achieve the broader aims of [Catholic] Religious Education outlined above. As a rough estimate, 25% of the GCSE would amount to around 10-15% of the curriculum in KS4 in a Catholic school.
If a child is excluded from RE or collective Christian worship at the behest of the parents it is not up to the parents to find an activity for the child to do. It is up to the school to supervise these children and find an alternative activity for them.
In my DCs' RC school in the US, any students not taking part in religious services had a study hall period, all the sitting out students in the same room with one teacher supervising, and they could do homework or sustained silent reading. My DN in Dublin sat out confirmation prep and read instead.
Amen to all of your posts here, Dahlietta 
She is not opposed to RE when it involves the academic study of religions and religious systems. She is opposed to participatory religious activities and activities that teach any sort of religion as objective truth, and wants to exercise her child's right and her right as a parent not to take part in those.