Failure to respond to two properly timed doses of MMR vaccine would be expected to occur in one or two persons per thousand vaccinees, at most. A small number of people appear to develop a relatively small amount of antibody following vaccination with rubella and other vaccines. This level of antibody may not be detectable on relatively insensitive commercial screening tests. I would suggest you make a note of her documented vaccination and stop testing. However, there are no data on the administration of additional doses of rubella-containing vaccine in this situation.
Joint symptoms are uncommon in children and in adult males.
Chronic joint symptoms attributable to rubella vaccine are very rare, if they occur at all. A PPD can be applied before or on the same day that MMR vaccine is given. However, if MMR vaccine is given on the previous day or earlier, the PPD should be delayed for at least one month. Live measles vaccine given prior to the application of a PPD can reduce the reactivity of the skin test because of mild suppression of the immune system. The effect of the nonsimultaneous administration of MMR and varicella is unknown, but there is theoretical concern that the vaccine given first could reduce the response to the vaccine given second.