WordPress Login for Another Web Designer

If you gave her your login info and she cannot login maybe you have a security plugin or something else in place that's restricts it to an IP?
Really don't know without more details.

However... You shouldn't ever be giving out your own login info...ever.
No need to do this.

Whenever you need to give someone else access to the admin area, create a login just for them with the correct "role" needed to accomplish the task.

This can be done without plugins but for ease of use and speed use a role plugin such as:

Members by Justin Tadlock (Awesome well coded plugin)
or
User Role Editor by Vladimir Garagulya

Both are free and will allow you to create a custom role for your designer.
It's highly unlikely they need full admin access... although it's possible.

So, create a new role and call it whatever you like... Example: "Designer".
Then you assign what they can edit or do within admin.

After you create the role, create a new user using her name and email.
Now she can login and in the future if you want to delete that user you can easily.

Yes you add a new role under the admin menu Users > Add new role
and you can see the roles under Users > roles.
This assumes your using the "Members" role plugin.

As far as what roles to assign for the task I'm not sure as I'm not using woocommerce.
I do know that there are capabilities specific to woocommerce added.
You'll see them when adding a new role when you assign capabilities.
Make sure to test the new role and login before giving it to her to make sure the task can be done.

Just logout and log back in with the new username/pass. If you can't edit as expected, there is a capability missing.