Am I being unreasonable?

Honey, your friend is the one being unreasonable here. You cannot sacrifice and endanger your health just to see her children, surely she should be able to understand that. If she does not, you need to consider how important this "friendship" is to you. Realistically, a visit could land you in the hospital, not a high risk that is worth taking. Any real friend should understand and respect that and say she looks forward to visiting with you at a better time.