Commercial lease: how to serve the 5 day notice in IL

[Helen Lee]

Unbelievalbe that I have to evict a tenant with good credit. She rented our storefront for storage. Last year, everything is ok. But ever since this Feb, she did not pay the rent. She said she was ill and in hospital. And she need heart transplant. I felt sorry for her and did not serve her any notice. And she kept promising me that she would move out. But she never did. Now I can't not handle this any more. And she just did not return my phone call or text. So I decided to start eviction. Here is my question. How could I serve her? She was ill and god knows where she would be, hospital? assisted living? In the commercial lease, there is a term as following:

Notices. Except as otherwise required by law, all notices under this Commercial Lease from Landlord to Tenant shall be mailed by first class U.S. mail, postage pre-paid, to Tenant’s last known address, or e-mailed to the e-mail address provided by Tenant in the Terms and Conditions and shall be conclusively presumed to have been received by Tenant three (3) business days after mailing or emailing. All notices from Tenant to Landlord shall be mailed by first class U.S. mail, postage pre-paid, to Landlord, at the PO Box address of the Facility listed on the first page of this Commercial Lease. Tenant is responsible for notifying Landlord in writing, via certified mail return receipt requested or via notice in the drop box, on a form prescribed by Landlord of any change in Tenant’s address or of intent to vacate at the end of the term.

Can I just send a first class mail for to serve the 5-day notice?

Anyone has suggestions?