Mrs. Shobha is leaving to Delhi this evening/by this evening.

Dear sir,

Mrs. Shobha is leaving for Delhi this evening.

Mrs. Shobha is leaving for Delhi by this evening.

Which one is correct in the above sentences?

Thanks in advance.

Sweetie

both are okay, but they have different meanings.
"Mrs. Shoba is leaving to Delhi by this evening"
::means that she is leaving no later than, or before this evening - maybe she will leave in the morning or the afternoon.
"Mrs. Shoba is leaving to Delhi this evening" means that she will leave at that time, and no other time.
hth.