Your mother is not in control. She needs to play by UPS rules, or use another shipper. It is really that simple. I live in the boondocks, so I have had to learn how to use UPS. I have, and everything works very well, described below.

It is not the driver's choice to require a signature. If the shipper (sender) says a signature is not required, then the driver can leave the package if nobody is home. But if a signature is required by the sender, the driver can't leave it.

One time in my life, a package disappeared. It was from LL Bean. I called Bean, and they said "Ok, that is fine. We don't require UPS to get a signature, so someone must have taken it. We will just send another one."

You have several choices. There is no need to do a "reroute," your mother can simply have the package sent to her work address from the start. I have done this many times in my life, and it worked great. If this is frowned upon by her company, choice #2:

Have the package sent to the UPS hub in c/o her name. Instruct the shipper to write "Hold for pickup" on the box, and a telephone number. I have done this several times, and it also works great. If this is not acceptable, choice #3:

Use online tracking, and be at home! This also works very reliably. If this is no good, choice #4:

Use somebody else.

You can't call the shots with UPS. It doesn't work that way.