It's against the rules for ICANN to do something like that. You must provide valid information. Besides, lets say someone hijacks the domain name, with invalid information, how's she going to prove that the domain is really hers.
If she wants things to be private, you can use privacy protection - most domain registrars off this for free (some still charge $8/year). X'ing out the information or putting false information is also invalid.
If you report the WHOIS information as being invalid, the registrar can suspend the domain name from operation.
Follow the rules: http://www.icann.org/en/topics/whois-services/
To report a bad WHOIS information, please go to http://wdprs.internic.net/