A little more info would be helpful. Things like:
Is your new computer running XP Pro?
Has Simple File Sharing been disabled?
If so, did you create an account for your wife on this computer?
Does it have the same user name and password as her account on
her computer?
If you didn't disable Simple File Sharing did you make any
changes to the Guest account?
Did you setup an Account Lockout Policy in the Local Security
Settings?
When you first tried to access this folder from the your computer
were you asked to enter a password?
The behavior you describe would happen when too many logon
attempts have been made with the wrong password. Once the
threshold set in the Account Lockout policy has been reached the
account is disabled and can only be unlocked by an administrator.
To check on the password issue:
On your computer, go to Administrative Tools in Control Panel and
open Computer Management.
Under Local Users and Groups expand the Users folder.
Right click your wife's account and see if the "Account is
disabled" box is checked.
If it is, uncheck it.
From there you can also reset her password so it agrees with the
one she uses on her machine.
If you haven't disabled Simple File Sharing then I'd suggest you
start to take a look at the built-in Guest account as the source
of the problem. If that's the case then you might want to try the
following:
Go to Start -> Run. Enter cmd.exe in the Open box.
Enter "net user guest" (leaving out the quotes) in the Command
Prompt window and hit enter.
Look for a line that reads "Account active Yes".
Note: You should also check to make sure that the line "Password
expires" is set to Never and "Password Required" is set to No.
If "Account active" is set to No then type the following (leaving
out the quotes) and hit enter.
"net user guest/active:yes"
If you're running XP Pro check your Local Security Policy (look
in Control Panel -> Administrative Tools). Navigate to Local
Policies\User Rights Assignment and right click the entry in the
right pane for "Deny access to this computer from the network".
Make sure the Guest account is not listed.
If none of this helps then post back with answers to the
questions I posed at the beginning.