I think that what you want from her are only the personal e-mails that she sends you and not the forwards and jokes ... etc.
Depending on what is being sent, you could do one of the following ...
1. If the messages to the 'group' all have something in the subject line that identifies it like a forward ... etc. you could create a rule to catch them.
1.a. If she sends them to the same multiple people, you can create a rule that if it contains all of the people in a list you can do whatever you want with it. This might not work if she modifies her distribution list though.
2. Ask her to make sure she puts a unique identifier in the subject so you can filter them out with a rule.
3. Ask her to not include you in her 'whatever' (joke ... etc) mailing list (this has worked best for me)
4. Just deal with it and delete them when they arrive.
If you choose #3, just be open and honest with her. Most people understand and quit sending 'garbage/junk/jokes' but still send the personal letters.
I hope this helps.
I am using Outlook 2003. I have a lady that sends me emails that go to a distribution list that I am apparently on. Occasionally she sends me things that are personal, so I don't want to block emails from here entirely, just emails that are to multiple people, from her. I am on other people's distribution list that I want to be on, so I don't want to block all emails that aren't sent just to me, just the ones that are from her. Hope this isn't too confusing. I'm sure there has to be a rule in Outlook that can do what I want, but I haven't figured it out. Please reply if you are knowledgable! Thanks!

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic