Relative has high eosinophilia, she also has lymphnodes swollen in mediastinal, she has asthma & history bronchitis,is this concern 4 eosinophilic leukemia?

Not really: To me it's a concern that the underlying causes for her asthma and "bronchitis" are not being addressed. Allergies will cause eosinophilia and al of the other things you describe, either directly or indirectly. I'd start with a visit to an allergist for evaluation and treatment modification, as these things indicate less than perfect control.

Yes, but rare: Usually elevated eosinophils are due to allergic problems ( asthma, allergic rhinitis) & certain infections. Given the above history, allergic aspergillosis is a consideration ( that's an exaggerated immune response to a certain fungus ). Eosinophilic leukemia is rare, but would be in the differential diagnosis.

How high?: The workup is really between her and her physician, but if this is new-onset asthma in an adult with really high blood eosinophilia and she's clearly sick, it's Churg-Strauss until proved otherwise.

If that worried for : cancer...ease of mind and see oncologist. Eosinophils can go up with parasite infections. Need a stool for O and P. repeat test in a week.