depends where you are...here in hampshire its lovely during the day but still too cold at night, further north it might still be too cold in the day time too. Even allowing for "normal" weather, you can't reliably put tender plants out until May. If she decides to risk it, she should make sure that they are in a position to get maximum sun (should do that for geraniums anyway) and either take in at night or wrap in fleeece overnight. In any case, the bigger the plant, the better the chance of success.