My mother have rheumatoid arthritis and her doctor prescribed methotrexate & adalimumab (sub-q), did this combination too heavy for health or normal?

No. This is appropriate combination therapy for uncontrolled ra. The benefits of these meds in preventing joint damage and disability far outweighs the risks.
Depends. Depends on the severity of her disease, several medications are available to treat ra. She needs to be closely monitored for side effects but she should be fine.